Update ReactiveSwift to 3.1 and ReactiveCocoa to 7.1

Author: james-lukanta-ck

.travis.yml

@@ -1,6 +1,6 @@
 language: objective-c
 cache: cocoapods
-osx_image: xcode8.3
+osx_image: xcode9.3
 before_install:
   - brew uninstall carthage
   - HOMEBREW_NO_AUTO_UPDATE=1 brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/6ae4f69a652fb0ecb102b0c9216378679a4f1b92/Formula/carthage.rb # 0.22.0

Cartfile

@@ -1,2 +1,2 @@
-github "ReactiveCocoa/ReactiveSwift" ~> 2.0
-github "ReactiveCocoa/ReactiveCocoa" ~> 6.0
+github "ReactiveCocoa/ReactiveSwift" ~> 3.1
+github "ReactiveCocoa/ReactiveCocoa" ~> 7.1

Cartfile.resolved

@@ -1,6 +1,6 @@
-github "Quick/Nimble" "v7.0.1"
-github "Quick/Quick" "v1.1.0"
-github "ReactiveCocoa/ReactiveCocoa" "6.0.0"
-github "ReactiveCocoa/ReactiveSwift" "2.0.0"
-github "antitypical/Result" "3.2.3"
+github "Quick/Nimble" "v7.1.1"
+github "Quick/Quick" "v1.2.0"
+github "ReactiveCocoa/ReactiveCocoa" "7.2.0"
+github "ReactiveCocoa/ReactiveSwift" "3.1.0"
+github "antitypical/Result" "3.2.4"
 github "jspahrsummers/xcconfigs" "0.10"