The folks over at drone.io offer free builds for open source projects. However, currently they only support Go 1.2. This method allows you to to cross-compile artifacts with a more recent version of Go.
Copy commands.sh and environment-variables.sh into the Settings / Build & Test tab and copy artifacts.sh into the Settings / Artifacts tab. Then, adjust the GOX_OSARCH environment variable to your liking.
Incidentally, I specified that my project is C / C++ for the simple reason that gox recompiles the build toolchain.