Update to C++17

Author: cherylEnkidu

FirebaseFirestoreInternal.podspec

@@ -115,7 +115,7 @@ Google Cloud Firestore is a NoSQL document database built for automatic scaling,
 
   s.library = 'c++'
   s.pod_target_xcconfig = {
-    'CLANG_CXX_LANGUAGE_STANDARD' => 'c++14',
+    'CLANG_CXX_LANGUAGE_STANDARD' => 'c++17',
     'CLANG_CXX_LIBRARY' => 'libc++',
     'GCC_PREPROCESSOR_DEFINITIONS' =>
       "FIRFirestore_VERSION=#{s.version} " +

Firestore/Example/GoogleService-Info.plist

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>API_KEY</key>
+	<string>AIzaSyAhb_3k3MyKrCTlfkMomysi-8UaICBSnrw</string>
+	<key>GCM_SENDER_ID</key>
+	<string>323991545240</string>
+	<key>PLIST_VERSION</key>
+	<string>1</string>
+	<key>BUNDLE_ID</key>
+	<string>iOSTestApp</string>
+	<key>PROJECT_ID</key>
+	<string>firestore-sdk-nightly</string>
+	<key>STORAGE_BUCKET</key>
+	<string>firestore-sdk-nightly.appspot.com</string>
+	<key>IS_ADS_ENABLED</key>
+	<false></false>
+	<key>IS_ANALYTICS_ENABLED</key>
+	<false></false>
+	<key>IS_APPINVITE_ENABLED</key>
+	<true></true>
+	<key>IS_GCM_ENABLED</key>
+	<true></true>
+	<key>IS_SIGNIN_ENABLED</key>
+	<true></true>
+	<key>GOOGLE_APP_ID</key>
+	<string>1:323991545240:ios:5f550d7ae3ebb43a1cf7ed</string>
+</dict>
+</plist>

Firestore/Example/ProtobufCpp.podspec

@@ -62,7 +62,7 @@ Pod::Spec.new do |s|
 
   # Set a CPP symbol so the code knows to use framework imports.
   s.pod_target_xcconfig = {
-    'CLANG_CXX_LANGUAGE_STANDARD' => 'c++14',
+    'CLANG_CXX_LANGUAGE_STANDARD' => 'c++17',
     'GCC_PREPROCESSOR_DEFINITIONS' =>
       '$(inherited) ' +
       'GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1 ' +