Bump version to 3.1.0.

Author: manastungare

src/manifest.json

@@ -2,7 +2,7 @@
   "manifest_version": 2,
   "name": "__MSG_google_calendar_extension_name__",
   "description": "__MSG_google_calendar_extension_desc__",
-  "version": "3.0.1",
+  "version": "3.1.0",
   "default_locale": "en",
   "key": "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCzO8gAn6n4s5Ohs50F2lmLGsO0FVKIwYyro8qZHlU+9pF85wGBEqoNwSeawr+AZdLgtnQRkIgatLM68EX8sB0DErp3Ds4qCvY8VufvvDIoqxdKtC3QlFxR9PoUZMY7/4lb/OadWnr0UjekxcSNVyk6nqZkTFCcE7RWDMDZ8qwqsQIDAQAB",
   "icons": {