Ignore SDK CPP build directory (#2284)
Ignore SDK CPP build directory (#2284)

test/sdk/cpp/sdk/ gets generated on CPP SDK testing, but depending on
your dev path, may not get cleaned up (and you may not want it to be
cleaned up).

So finally adding it to .gitignore rather than forcing myself to delete
it every time.
googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones