fix package syntax

Author: morganchen12

Package.swift

@@ -72,7 +72,7 @@ let package = Package(
     .package(
       name: "Firebase", 
       url: "https://github.com/firebase/firebase-ios-sdk.git",
-      from: "8.0.0"..<"10.0.0"
+      "8.0.0"..<"10.0.0"
     ),
     .package(
       name: "GoogleSignIn",