Change generated binary to 1.18

[abice]

Since the syntax parsing is so different in 1.18, the binary now needs to be released using go 1.18.

I still have all the previous versions of go building the lib, so it should be backwards compatible.

[coveralls]

Coverage increased (+5.6%) to 93.016% when pulling eba8f4b on abice/go118 into ff7c099 on master.