Gutter isn't updated when a single screen line is modified.

src/atom/editor.coffee

@@ -177,10 +177,11 @@ class Editor extends View
       @cursor.bufferChanged(e)
 
     @renderer.on 'change', (e) =>
-      @gutter.renderLineNumbers(@getScreenLines())
+      { oldRange, newRange } = e
+      unless newRange.isSingleLine() and newRange.coversSameRows(oldRange)
+        @gutter.renderLineNumbers(@getScreenLines())
 
       @cursor.refreshScreenPosition() unless e.bufferChanged
-      { oldRange, newRange } = e
       screenLines = @linesForRows(newRange.start.row, newRange.end.row)
       if newRange.end.row > oldRange.end.row
         # update, then insert elements

src/atom/range.coffee

@@ -31,6 +31,12 @@ class Range
 
     other.start.isEqual(@start) and other.end.isEqual(@end)
 
+  isSingleLine: ->
+    @start.row == @end.row
+
+  coversSameRows: (other) ->
+    @start.row == other.start.row && @end.row == other.end.row
+
   inspect: ->
     "[#{@start.inspect()} - #{@end.inspect()}]"