Fix broken file extensions in paths

[rdner]

Before this change when running go-licenser with the -exclude flag
pointing to a file, the exclusion rule would never work. When walking the
directory currentPath was always losing the first . which
corrupted file extensions.

For example,

./go-licenser -exclude "pkg/proto/messages/struct.pb.go" -license
"Elastic" -ext ".go"

was always replacing the license header in
pkg/proto/messages/struct.pb.go because while walking the
currentPath would become pkg/proto/messages/structpb.go.

After this change currentPath is trimmed from the start only.

[elasticmachine]

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• Start Time: 2022-06-28T18:39:26.333+0000

• Duration: 4 min 24 sec

[zenitraM]

LGTM so now it only replaces the string at the beginning and not everywhere.

Not sure of the entire logic around this code but won't this be an issue when specifying paths like ./foo gets replaced to /foo? or when a file is hidden like .test.go? -- this was also happening on the old logic, though, so this doesn't really make it worse.

Maybe a further fix could be to make ./ the default path instead of just .

[rdner]

@zenitraM I ran go-licenser without specifying a path, so I assume it used the default one defined in the constant. After this fix I didn't have any issues but I might have missed some edge cases, indeed. Let's keep it like this for now. If I (or someone else) find another issue we can fix it separately. At least there should be no regression.