Updated wpxmlrpc to 0.4.1 to include WPStringUtils fix

Also updated CocoaLumberjack to 1.8.1 and removed duplicate lines from Podfile.
Merge branch 'develop' into issue/1448-update-wpxmlrpc

Conflicts:
	Podfile
	Pods/Pods-NSLogger-Private.xcconfig
	Pods/Pods.xcconfig
	Pods/Pods.xcodeproj/project.pbxproj
Merge pull request #1451 from wordpress-mobile/issue/1448-update-wpxmlrpc

Update wpxmlrpc CocoaPod to get fix for crashes