Fix path encoding when it contains brackets

Files (like swagger 1.0 JSON descriptors) which are on a path containing "{" or "}" in their name are not correctly encoded. They should be encoded to %7B and %7D accordingly to correctly follow URI standards. Tomcat currently throws an 500 HTTP code if receiving not correctl encoded URIs.
Merge pull request #68 from Antronin/patch-1

[loopback:swagger] Fix path encoding when it contains brackets