Fix default date format string at startup

Not sure what happened when I tried to do this in 39133b1, but evaluating
`DEFAULT_DATE` at import time doesn't work because `atom.config.get` returns
undefined. So calculate it later and cache it.

Test Plan:
Reloaded window then opened blame in a big file. Saw my preferred datestring
and not the full ISO 8601 format.

Author: dmnd

lib/util/blameFormatter.js

@@ -28,6 +28,7 @@ function parseCommitter(line) {
  */
 function formatDate(date) {
   var formatString = atom.config.get('git-blame.dateFormatString');
+  console.log(formatString);
   return date.format(formatString);
 }
 

lib/views/blame-line-view.coffee

@@ -6,13 +6,16 @@ moment = require 'moment'
 
 HASH_LENGTH = 7  # github uses this length
 BLANK_HASH = '-'.repeat(HASH_LENGTH)
-DEFAULT_DATE = formatDate moment("2000-01-01T13:17:00 Z")
+
+_defaultDate = null
+getDefaultDate = ->
+  _defaultDate ?= formatDate moment("2014-01-01T13:37:00 Z")
 
 
 renderLoading = ->
   div className: 'blame-line loading',
     span className: 'hash', BLANK_HASH
-    span className: 'date', DEFAULT_DATE
+    span className: 'date', getDefaultDate()
     span className: 'committer', 'Loading'