electron flow type definitions

Summary: Adding a flowtype library definition for electron 3 and fixing related type errors

Reviewed By: passy

Differential Revision: D9124758

fbshipit-source-id: e09cb5b05ba952e7f95f68f9043edc586f81ae83

src/utils/isProduction.js

@@ -8,6 +8,7 @@
 import electron from 'electron';
 
 const _isProduction = !/node_modules[\\/]electron[\\/]/.test(
+  // $FlowFixMe: execPath exists, but is not in electron API spec
   electron.remote.process.execPath,
 );