Fix signature for URLs that contain colons (:)

[matiasgarciaisaia]

s3browser is generating links with the wrong signature if the file path includes a colon.

This can be tested by creating a file test.txt and another text:colons.txt in the bucket root, and running the project with S3_SIGNED_URL=true. The link for test.txt works, but the one for text:colons.txt results in a SignatureDoesNotMatch error.