fix typo in overlay.js

Author: marijnh

lib/overlay.js

@@ -46,6 +46,6 @@ CodeMirror.overlayParser = function(base, overlay, combine) {
     indent: function(state, textAfter) {
       return base.indent(state.base, textAfter);
     },
-    electricChars: base.electicChars
+    electricChars: base.electricChars
   };
 };