Add "darwin" option to so npm test runs on mac

Author: yj7o5

package.json

@@ -12,7 +12,8 @@
     "test": "cross-os _test ",
     "_test": {
       "win32": "tsc -p tsconfig.test.json && copy test\\Assets\\* .test\\test\\Assets && mocha .test\\test",
-      "linux": "tsc -p tsconfig.test.json && cp test/Assets/* .test/test/Assets && mocha .test/test"
+      "linux": "tsc -p tsconfig.test.json && cp test/Assets/* .test/test/Assets && mocha .test/test",
+      "darwin": "tsc -p tsconfig.test.json && cp test/Assets/* .test/test/Assets && mocha .test/test"
     },
     "build": "tsc",
     "build:test": "tsc -p tsconfig.test.json",