Specify RxCocoa to 4.x for tests

Author: kylefleming

test/change_podfile.py

@@ -53,7 +53,7 @@ def addSwiftPod():
 """
 keep_source_code_for_prebuilt_frameworks!
 
-pod "RxCocoa", :binary => true
+pod "RxCocoa", "~> 4.0", :binary => true
 pod "Literal", :binary => true
 """), 
 """
@@ -70,7 +70,7 @@ def revertToSourceCode():
 """
 keep_source_code_for_prebuilt_frameworks!
 
-pod "RxCocoa", :binary => true
+pod "RxCocoa", "~> 4.0", :binary => true
 pod "Literal"
 """), 
 """