[r mode] Add lineComment property

Author: vincentwoo

mode/r/r.js

@@ -138,7 +138,9 @@ CodeMirror.defineMode("r", function(config) {
       if (ctx.type == "block") return ctx.indent + (firstChar == "{" ? 0 : config.indentUnit);
       else if (ctx.align) return ctx.column + (closing ? 0 : 1);
       else return ctx.indent + (closing ? 0 : config.indentUnit);
-    }
+    },
+
+    lineComment: "#"
   };
 });