src/parser.pegjs: Use strict comparison

Fixes the following JSHint errors:

  ./src/parser.js: line 460, col 50, Expected '!==' and instead saw '!='.
  ./src/parser.js: line 486, col 42, Expected '!==' and instead saw '!='.

src/parser.js

@@ -457,7 +457,7 @@ PEG.parser = (function(){
         }
         if (result0 !== null) {
           result0 = (function(elements, code) {
-                var expression = elements.length != 1
+                var expression = elements.length !== 1
                   ? {
                       type:     "sequence",
                       elements: elements
@@ -483,7 +483,7 @@ PEG.parser = (function(){
           }
           if (result0 !== null) {
             result0 = (function(elements) {
-                  return elements.length != 1
+                  return elements.length !== 1
                     ? {
                         type:     "sequence",
                         elements: elements

src/parser.pegjs

@@ -50,7 +50,7 @@ choice
 
 sequence
   = elements:labeled* code:action {
-      var expression = elements.length != 1
+      var expression = elements.length !== 1
         ? {
             type:     "sequence",
             elements: elements
@@ -63,7 +63,7 @@ sequence
       };
     }
   / elements:labeled* {
-      return elements.length != 1
+      return elements.length !== 1
         ? {
             type:     "sequence",
             elements: elements