Set minimum Chrome version to 42.

It would seem there's an ABI change in version 43 of the SDK, which prevents
PNaCl from loading on Chrome 41. Setting the minimum Chrome version should
prevent older browsers from updating or installing.

src/manifest.json.template

@@ -1,10 +1,10 @@
 {
   "manifest_version": 2,
-  "minimum_chrome_version": "31",
+  "minimum_chrome_version": "42",
   "name": "${NAME}",
   "description": "${DESCRIPTION}",
   "offline_enabled": true,
-  "version": "0.2.10.${BUILD_NUM}",
+  "version": "0.2.11.${BUILD_NUM}",
   "app": {
     "background": {
       "scripts": ["background.js"]