Update .gitmodules to work with latest version of git

[adamgall]

Sometime between git version 2.19.0 and 2.22.0 git changed the way it parses repository URLs in .gitmodules, and now swift-protobuf won't update after git submodule initing with the slash-ending URL.

Fixed by updating the url for swift-protocol to end in .git instead of / in .gitmodules

Was receiving error:

$ git submodule init
Submodule 'Modules/breadwallet-core' (https://github.com/breadwallet/breadwallet-core.git) registered for path 'Modules/breadwallet-core'
Submodule 'Modules/swift-protobuf' (https://github.com/breadwallet/swift-protobuf/) registered for path 'Modules/swift-protobuf'

$ git submodule update
Cloning into '.../breadwallet-ios/Modules/breadwallet-core'...
Cloning into '.../breadwallet-ios/Modules/swift-protobuf'...
ERROR: Repository not found.
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
fatal: clone of 'https://github.com/breadwallet/swift-protobuf/' into submodule path '.../breadwallet-ios/Modules/swift-protobuf' failed
Failed to clone 'Modules/swift-protobuf'. Retry scheduled
Cloning into '.../breadwallet-ios/Modules/swift-protobuf'...
ERROR: Repository not found.
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
fatal: clone of 'https://github.com/breadwallet/swift-protobuf/' into submodule path '.../breadwallet-ios/Modules/swift-protobuf' failed
Failed to clone 'Modules/swift-protobuf' a second time, aborting

[anasoid]

I have the same problem using submodule