Throw error for reserved words enum and await (#195)

* Throw error for reserved words enum and await when source type is module

* Extract reserved word check into method

* Fix tests

test/fixtures/esprima/es2015-arrow-function/invalid-param-strict-mode/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Binding eval in strict mode (1:0)"
-}
+  "throws": "eval is a reserved word in strict mode (1:0)"
+}