Updated GTMSessionFetcher package version

The version is now the same as the Firebase-iOS-SDK.

Author: ArturoLee

Package.swift

@@ -87,7 +87,7 @@ let package = Package(
     .package(
       name: "GTMSessionFetcher",
       url: "https://github.com/google/gtm-session-fetcher.git",
-      "1.4.0" ..< "2.0.0"
+      "2.1.0" ..< "3.0.0"
     ),
     .package(
       name: "SDWebImage",