Bump version to 4.1.0 to go with minOS change.

This doesn't have to be a new major because we're added back support for
something removed, so it expands the compatibility vs. reduces it.

GTMSessionFetcher.podspec

@@ -2,7 +2,7 @@
 # to import GTMSessionFetcher via the CocoaPods dependency Manager.
 Pod::Spec.new do |s|
  s.name = 'GTMSessionFetcher'
- s.version = '4.0.0'
+ s.version = '4.1.0'
  s.authors = 'Google Inc.'
  s.license = { :type => 'Apache', :file => 'LICENSE' }
  s.homepage = 'https:/google/gtm-session-fetcher'