reuse existing cocoapods

move carthage version to deploy

remove pod version as it is already announced as part of the normal build:
https://travis-ci.org/paulz/PerspectiveTransform/builds/348443168 (+10 squashed commits)
Squashed commits:
[5266b7e] cleanup travis script
[424663f] remove rvm and bundle

to use existing cocoapods
[897a05d] skip installing slather on travis
[c405709] reuse existing bundler
[da5271e] shoe bundle version
[0526b4e] use the same version of cocoapods as on travis
[5314398] remove cocoapods gem to reuse existing on travis
[6900b88] log rvm gems
[a2476a3] Update .travis.yml

Remove RVM to use default
[1a6478c] show cocoapods version

PerspectiveTransform.podspec

@@ -1,5 +1,5 @@
 Pod::Spec.new do |s|
-  s.cocoapods_version = '>=1.4.0'
+  s.cocoapods_version = '>= 1.3.1'
   s.name              = 'PerspectiveTransform'
   s.version           = '0.2.0'
   s.summary           = 'Perspective Transform calculates CATransform3D'
@@ -16,7 +16,6 @@ Pod::Spec.new do |s|
   s.social_media_url  = 'https://twitter.com/iospaulz'
 
   s.platform      = :ios, '11.0'
-  s.swift_version = '4.0'
   s.source_files  = 'Pod/Classes/**/*'
   s.frameworks    = 'UIKit', 'CoreGraphics', 'QuartzCore'
 end