Relative path in wavfile_test.go

[Shion1305]

Relative path are used in wavfile_test.go.

https://github.com/sunicy/go-lame/blob/1c192eaafa399fe3eca1d930790b66a48f2a4c73/wavfile_test.go#L6 However relative path imports are not allowed since Go 1.11

When I try to use this package, following error occurs.

	github.com/sunicy/go-lame tested by
	github.com/sunicy/go-lame.test imports
	./compare: "./compare" is relative, but relative import paths are not supported in module mode