Rename 'finish-launching' event to 'ready',

'finish-launching' is more like a OS X message name, and in atom-shell
it means initialization has done, so 'ready' seems to be a better name
and more easy to remember.

The 'will-finish-launching' event just represents the corresponding
message on OS X and is the same with 'ready' on other platforms, so we
keep its name to indicate that it's only useful for OS X specified
code.

spec/static/main.js

@@ -40,7 +40,7 @@ app.on('window-all-closed', function() {
   app.terminate();
 });
 
-app.on('finish-launching', function() {
+app.on('ready', function() {
   var template = [
     {
       label: 'Atom',