Update swift-protobuf dependency (#4587)

Author: paulb777

ZipBuilder/Package.swift

@@ -26,7 +26,9 @@ let package = Package(
     .executable(name: "UpdateFirebasePod", targets: ["UpdateFirebasePod"]),
   ],
   dependencies: [
-    .package(url: "https://github.com/apple/swift-protobuf.git", .exact("1.2.0")),
+    // Keep the generated protos in sync with the version below.
+    // See https://github.com/firebase/firebase-ios-sdk/tree/master/ZipBuilder#updating-protobuf-generated-swift-files.
+    .package(url: "https://github.com/apple/swift-protobuf.git", .exact("1.7.0")),
   ],
   targets: [
     .target(