Update tools/generate-identifier-regex.js

So that it can also spit out the astral maps.

src/expression.js

@@ -491,7 +491,7 @@ pp.parsePropertyName = function(prop) {
   if (this.options.ecmaVersion >= 6) {
     if (this.eat(tt.bracketL)) {
       prop.computed = true
-      prop.key = this.parseExpression()
+      prop.key = this.parseMaybeAssign()
       this.expect(tt.bracketR)
       return
     } else {