title: Double question mark (??) help search not working in RStudio (and RStudio only)
body: <p>strange behaviour I noticed in my RStudio installation:</p>
  
  <ul>
  <li>Help search via the double question mark (e.g., <code>??gg</code>) does not work in RStudio. It gives me "No results found" in the Help pane.</li>
  <li>Help search via the upper search field in the Help pane works as intended and returns results for the example search above.</li>
  <li><code>??</code> works in the Mac OS R GUI ("R.app"), it opens a browser tab with the results page.</li>
  <li>Single question mark <code>?</code> works also in RStudio (but of course only with exact matches to names).</li>
  </ul>
  
  <p>Does anybody know how to resolve this? Thanks!</p>
  
  <p>EDIT: My <code>sessionInfo()</code>:</p>
  
  <pre><code>R version 3.6.0 (2019-04-26)
  Platform: x86_64-apple-darwin15.6.0 (64-bit)
  Running under: macOS Mojave 10.14.6
  
  Matrix products: default
  BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
  LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib
  
  locale:
  [1] de_DE.UTF-8/de_DE.UTF-8/de_DE.UTF-8/C/de_DE.UTF-8/de_DE.UTF-8
  
  attached base packages:
  [1] parallel  stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] jsonlite_1.6         scales_1.0.0         tidyr_0.8.3          ggplot2_3.2.0        koRpus.lang.de_0.1-1 koRpus_0.11-5       
  [7] sylly_0.1-5          readxl_1.3.1         data.table_1.12.2   
  
  loaded via a namespace (and not attached):
   [1] Rcpp_1.0.1       highr_0.8        cellranger_1.1.0 pillar_1.4.1     compiler_3.6.0   tools_3.6.0      zeallot_0.1.0   
   [8] digest_0.6.19    tibble_2.1.3     gtable_0.3.0     pkgconfig_2.0.2  rlang_0.4.0      cli_1.1.0        rstudioapi_0.10 
  [15] curl_3.3         yaml_2.2.0       xfun_0.8         knitr_1.23       withr_2.1.2      dplyr_0.8.1      vctrs_0.1.0     
  [22] grid_3.6.0       tidyselect_0.2.5 sylly.de_0.1-2   glue_1.3.1       R6_2.4.0         fansi_0.4.0      purrr_0.3.2     
  [29] magrittr_1.5     backports_1.1.4  fortunes_1.5-4   assertthat_0.2.1 colorspace_1.4-1 labeling_0.3     utf8_1.1.4      
  [36] lazyeval_0.2.2   munsell_0.5.0    crayon_1.3.4
  </code></pre>