title: r-mapview legend name in multiple lines
body: <p>I am trying to create a legend with multiple lines as shown in <a href="https://stackoverflow.com/questions/53147085/leaflet-legend-name-in-two-lines/53147231#53147231">this leaflet example</a>, but using the mapview package instead.</p>
  <p>Following the above example, these cases work fine:</p>
  <pre><code>
      library(leaflet)
      library(raster)
      library(mapview)
      
      p &lt;- shapefile(system.file(&quot;external/lux.shp&quot;, package=&quot;raster&quot;))
      
      pal &lt;- colorNumeric(
        palette = &quot;Reds&quot;,
        domain = p$AREA)
      
      p %&gt;% 
        leaflet() %&gt;% 
        addTiles() %&gt;% 
        addPolygons(stroke=FALSE, color = ~pal(AREA), fillOpacity = 1) %&gt;% 
        addLegend(pal = pal, values = ~AREA, title = &quot;line 1 &lt;/br&gt; line 2&quot;)
      
      p %&gt;%
        mapview(
          zcol = 'AREA',
          stroke = FALSE,
          alpha = 1,
          layer.name = &quot;line 1&quot;
        )
  
  </code></pre>
  <p>However, introducing the &lt;/br&gt; or &lt;br&gt; into the mapview layer.name introduces errors.</p>
  <pre><code>
      p %&gt;%
        mapview(
          zcol = 'AREA',
          stroke = FALSE,
          alpha = 1,
          layer.name = &quot;line 1 &lt;/br&gt; line 2&quot;
        )
      #Error in validateScalarName(name) : 
      #  Invalid argument 'name' (must be a non-empty character string and contain no '/' or '\')
      #In addition: Warning message:
      #In file.create(to[okay]) :
      #  cannot create file 'C:/RTMP\Rtmp6rsB0P\file2a687e904718/line1&lt;/br&gt;line2_layer.fgb', reason #'Invalid argument'
  
  </code></pre>
  <pre><code>
      p %&gt;%
        mapview(
          zcol = 'AREA',
          stroke = FALSE,
          alpha = 1,
          layer.name = &quot;line 1 &lt;br&gt; line 2&quot;
        )
      #Error in normalizePath(path.expand(path), winslash, mustWork) : 
      #  path[1]=&quot;lib/line1&lt;br&gt;line2-0.0.1&quot;: The filename, directory name, or volume label syntax is #incorrect
      #In addition: Warning messages:
      #1: In file.create(to[okay]) :
      #  cannot create file 'C:/RTMP\Rtmp6rsB0P\file2a6843ec14e6/line1&lt;br&gt;line2_layer.fgb', reason #'Invalid argument'
      #2: In dir.create(target_dir) :
      #  cannot create dir 'lib\line1&lt;br&gt;line2-0.0.1', reason 'Invalid argument'
  
  </code></pre>
  <p>sessionInfo() below</p>
  <p><div class="snippet" data-lang="js" data-hide="true" data-console="false" data-babel="false">
  <div class="snippet-code snippet-currently-hidden">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>R version 4.0.3 (2020-10-10)
  Platform: x86_64-w64-mingw32/x64 (64-bit)
  Running under: Windows 10 x64 (build 19043)
  
  Matrix products: default
  
  locale:
  [1] LC_COLLATE=English_United States.1252 
  [2] LC_CTYPE=English_United States.1252   
  [3] LC_MONETARY=English_United States.1252
  [4] LC_NUMERIC=C                          
  [5] LC_TIME=English_United States.1252    
  
  attached base packages:
  [1] stats     graphics  grDevices datasets  utils    
  [6] methods   base     
  
  other attached packages:
  [1] mapview_2.10.0  raster_3.1-5    sp_1.4-5       
  [4] leaflet_2.0.4.1 shiny_1.6.0    
  
  loaded via a namespace (and not attached):
   [1] Rcpp_1.0.4.6            lattice_0.20-41        
   [3] leaflet.providers_1.9.0 png_0.1-7              
   [5] class_7.3-17            ps_1.6.0               
   [7] assertthat_0.2.1        digest_0.6.25          
   [9] utf8_1.2.1              mime_0.9               
  [11] R6_2.5.0                reprex_2.0.0           
  [13] stats4_4.0.3            evaluate_0.14          
  [15] e1071_1.7-3             highr_0.8              
  [17] pillar_1.6.0            rlang_0.4.10           
  [19] rstudioapi_0.13         miniUI_0.1.1.1         
  [21] callr_3.7.0             jquerylib_0.1.4        
  [23] rmarkdown_2.9           rgdal_1.5-23           
  [25] webshot_0.5.2           htmlwidgets_1.5.1      
  [27] munsell_0.5.0           compiler_4.0.3         
  [29] httpuv_1.6.1            xfun_0.24              
  [31] pkgconfig_2.0.3         base64enc_0.1-3        
  [33] clipr_0.7.0             htmltools_0.5.1.1      
  [35] tidyselect_1.1.0        tibble_3.1.1           
  [37] codetools_0.2-16        fansi_0.4.2            
  [39] dplyr_1.0.5             crayon_1.4.1           
  [41] withr_2.4.2             later_1.0.0            
  [43] sf_0.9-8                grid_4.0.3             
  [45] jsonlite_1.6.1          satellite_1.0.2        
  [47] xtable_1.8-4            lifecycle_1.0.0        
  [49] DBI_1.1.1               magrittr_2.0.1         
  [51] units_0.6-6             scales_1.1.0           
  [53] KernSmooth_2.23-17      cli_2.4.0              
  [55] cachem_1.0.5            farver_2.0.3           
  [57] renv_0.13.2             fs_1.5.0               
  [59] promises_1.1.0          bslib_0.2.5.1          
  [61] generics_0.0.2          ellipsis_0.3.1         
  [63] vctrs_0.3.7             RColorBrewer_1.1-2     
  [65] tools_4.0.3             leafem_0.1.3           
  [67] glue_1.4.2              purrr_0.3.4            
  [69] crosstalk_1.1.0.1       processx_3.5.2         
  [71] fastmap_1.1.0           yaml_2.2.1             
  [73] colorspace_1.4-1        classInt_0.4-3         
  [75] knitr_1.28              sass_0.4.0 </code></pre>
  </div>
  </div>
  </p>
  <p>Any advice on how to solve this?</p>