Upgrade semver to 4.3.3

TBR=arv@

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/2090

Closes #2090.

Author: johnjbarton

package.json

@@ -66,7 +66,7 @@
     "commander": "2.9.x",
     "glob": "5.0.x",
     "rsvp": "^3.0.13",
-    "semver": "4.3.2",
+    "semver": "^4.3.3",
     "source-map-support": "~0.2.8"
   },
   "devDependencies": {