Validate as sb3 first

A vast majority of projects we get are sb3, so try that first
Technically this might change behavior if a project is both, but that seems like an edge case not worth worrying about
As part of this the sb2 schema is now compiled only if sb3 validation failed, which should slightly help loading performance

lib/validate.js

@@ -8,22 +8,20 @@ var sprite3Schema = require('./sprite3_schema.json');
 ajv.addSchema(sb2Defs).addSchema(sb3Defs);
 
 module.exports = function (isSprite, input, callback) {
-    var validateSb2 = ajv.compile(isSprite ? sprite2Schema : sb2Schema);
     var validateSb3 = ajv.compile(isSprite ? sprite3Schema : sb3Schema);
+    var isValidSb3 = validateSb3(input);
+    if (isValidSb3) {
+        input.projectVersion = 3;
+        return callback(null, input);
+    }
 
+    var validateSb2 = ajv.compile(isSprite ? sprite2Schema : sb2Schema);
     var isValidSb2 = validateSb2(input);
-
     if (isValidSb2) {
         input.projectVersion = 2;
         return callback(null, input);
     }
 
-    var isValidSb3 = validateSb3(input);
-    if (isValidSb3) {
-        input.projectVersion = 3;
-        return callback(null, input);
-    }
-
     var validationErrors = {
         validationError: 'Could not parse as a valid SB2 or SB3 project.',
         sb3Errors: validateSb3.errors,