Upgrade to brave/electron 1.4.15

Fix #4932

Auditors: @bridiver

.npmrc

@@ -1,5 +1,5 @@
 runtime = electron
 target = 1.4.0
 target_arch = x64
-brave_electron_version = 1.4.14
+brave_electron_version = 1.4.15
 disturl = https://atom.io/download/atom-shell

tools/cibuild.py

@@ -5,7 +5,7 @@
 import sys
 import os.path
 
-BRAVE_ELECTRON = '1.4.14'
+BRAVE_ELECTRON = '1.4.15'
 UPSTREAM_ELECTRON = '1.4.0'
 SOURCE_ROOT = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
 TARGET_ARCH= os.environ['TARGET_ARCH'] if os.environ.has_key('TARGET_ARCH') else 'x64'