fix(release): Update mversion to 1.12

Running `npm run release` with current stack resulted in the following
error for me:

```
/home/tim/.nvm/versions/node/v10.11.0/bin/node[13632]: ../src/node_contextify.cc:628:static void node::contextify::ContextifyScript::New(const v8::FunctionCallbackInfo<v8::Value>&): Assertion `args[1]->IsString()' failed.
 1: 0x8d20d0 node::Abort() [/home/tim/.nvm/versions/node/v10.11.0/bin/node]
 2: 0x8d21a5  [/home/tim/.nvm/versions/node/v10.11.0/bin/node]
 3: 0x9075f7 node::contextify::ContextifyScript::New(v8::FunctionCallbackInfo<v8::Value> const&) [/home/tim/.nvm/versions/node/v10.11.0/bin/node]
 4: 0xb89f5b  [/home/tim/.nvm/versions/node/v10.11.0/bin/node]
 5: 0xb8bef2 v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*) [/home/tim/.nvm/versions/node/v10.11.0/bin/node]
 6: 0x1a2b66f5c01d
Aborted (core dumped)
```

Upgrading `mversion` to 1.12 fixes it.

Author: pixelastic

package.json

@@ -57,7 +57,7 @@
     "karma-sourcemap-loader": "^0.3.7",
     "karma-webpack": "^2.0.3",
     "mocha": "^3.4.1",
-    "mversion": "^1.10.1",
+    "mversion": "^1.12.0",
     "netlify": "^2.0.1",
     "node-static": "^0.7.8",
     "phantomjs-prebuilt": "^2.1.12",