Update Podfiles after 6.0.0 release (#2964)

Author: paulb777

Example/Podfile

@@ -17,8 +17,8 @@ target 'Core_Example_iOS' do
   platform :ios, '8.0'
 
   # The next line is the forcing function for the Firebase pod. The Firebase
-  # version's subspecs should depend on the component versions in their
-  # corresponding podspec's.
+  # version's subspecs should depend on the component versions in the
+  # corresponding podspec's in this repo.
   pod 'Firebase/CoreOnly', '6.0.0'
 
   target 'Core_Tests_iOS' do

Firestore/Example/Podfile

@@ -3,8 +3,8 @@
 #source 'https://github.com/CocoaPods/Specs.git'
 
 # Uncomment the next two lines for pre-release testing on public repo
-source 'https://github.com/Firebase/SpecsStaging.git'
-source 'https://github.com/CocoaPods/Specs.git'
+#source 'https://github.com/Firebase/SpecsStaging.git'
+#source 'https://github.com/CocoaPods/Specs.git'
 
 use_frameworks!