go : run `go mod tidy` before building examples + fix permissions (#296)

go : run `go mod tidy` before building examples + fix permissions (#296)

* run `go mod tidy` before building examples

Running `make examples` after cloning the repository gives the following
error:

```
...
[100%] Built target whisper
gmake[3]: Leaving directory '/tmp/exp/whisper.cpp/bindings/go/build'
gmake[2]: Leaving directory '/tmp/exp/whisper.cpp/bindings/go/build'
gmake[1]: Leaving directory '/tmp/exp/whisper.cpp/bindings/go/build'
Build example go-model-download
Build example go-whisper
examples/go-whisper/process.go:11:2: missing go.sum entry for module providing package github.com/go-audio/wav (imported by github.com/ggerganov/whisper.cpp/bindings/go/examples/go-whisper); to add:
        go get github.com/ggerganov/whisper.cpp/bindings/go/examples/go-whisper
make: *** [Makefile:26: examples/go-whisper] Error 1
```

* remove executable bit from various files