Fix tokenizing of regexps after .of

Closes #727

Author: marijnh

src/tokencontext.js

@@ -139,7 +139,7 @@ tt.star.updateContext = function(prevType) {
 
 tt.name.updateContext = function(prevType) {
   let allowed = false
-  if (this.options.ecmaVersion >= 6) {
+  if (this.options.ecmaVersion >= 6 && prevType != tt.dot) {
     if (this.value === "of" && !this.exprAllowed ||
         this.value === "yield" && this.inGeneratorContext())
       allowed = true

test/tests-harmony.js

@@ -16241,3 +16241,5 @@ test('for ([...foo, bar].baz in qux);', {
 testFail("var f;\nfunction f() {}", "Identifier 'f' has already been declared (2:9)", {ecmaVersion: 6, sourceType: "module"});
 
 test("function f() { var x; function x() {} }", {}, {ecmaVersion: 6, sourceType: "module"})
+
+test("a.of / 2", {}, {ecmaVersion: 6})