title: Problem with plotting projected sf points: ggplot's coordinate type and gridlines unexpected
body: <p>I am trying to plot a reprojected dataset and although the coordinates have been reprojected, ggplot persists in using a degrees lon-lat coordinate system.</p>
  
  <p>Here's a reproducible example:</p>
  
  <pre><code>library(sf)
  library(dplyr)
  library(ggplot2)
  
  set.seed(42)
  df &lt;- tibble(lon = runif(20, min = -73, max = -68),
               lat = runif(20, min = 41, max = 46))
  sf &lt;- st_as_sf(df, coords = c("lon", "lat"), crs = 4326, agr = "constant")
  
  # This plot has the expected lon-lat degree coords
  ggplot(sf) + geom_sf()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/09mRd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/09mRd.png" alt="This plot has the expected lon-lat degree coords"></a></p>
  
  <pre class="lang-r prettyprint-override"><code># Lambert equal-area projection
  laea_centered &lt;- "+proj=laea +lat_0=43.15268 +lon_0=-70.30744"
  coord_shift &lt;- "+x_0=12019341.4 +y_0=1730136"
  proj_ref &lt;- " +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs"
  laea_proj4 &lt;- paste(laea_centered, coord_shift, proj_ref, sep = " ")
  
  sf &lt;- st_transform(sf, crs = laea_proj4)
  
  # Glancing at the data, the transformation appears correct.
  sample_n(sf, 5)
  # Simple feature collection with 5 features and 0 fields
  # geometry type:  POINT
  # dimension:      XY
  # bbox:           xmin: 75403.74 ymin: 1109827 xmax: 248543.9 ymax: 1660612
  # epsg (SRID):    NA
  # proj4string:    +proj=laea +lat_0=-70.30744 +lon_0=43.15268 +x_0=12019341.4 +y_0=1730136 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
  # # A tibble: 5 x 1
  # geometry
  # &lt;POINT [m]&gt;
  # 1 (248543.9 1153107)
  # 2 (88341.34 1109827)
  # 3 (166449.3 1138656)
  # 4 (87832.83 1660612)
  # 5 (75403.74 1430964)
  
  # Still has geographic coordinates and reticule
  ggplot(sf) + geom_sf()
  </code></pre>
  
  <p>The points have been projected, but the plot is still using the geographic coordinates for the axes and reticule.</p>
  
  <p><a href="https://i.stack.imgur.com/qujfb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qujfb.png" alt="enter image description here"></a></p>
  
  <pre><code># Same as above, but I wouldn't expect it to be different
  # because ggplot takes the crs from the initial data argument.
  ggplot(sf) +
    geom_sf() +
    coord_sf(crs = laea_proj4)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/bshXV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bshXV.png" alt="enter image description here"></a></p>