Fix redirect to align with the documentation

[jcoyne]

Previously it was redirecting to a full URI, but the documentation of the method indicates it should redirect to a path.

See documentation:

cantaloupe/src/main/java/edu/illinois/library/cantaloupe/resource/TrailingSlashRemovingResource.java

Lines 10 to 11 in 646e89b

	* Permanently redirects (via HTTP 301) {@literal /some/path/} to {@literal
	* /some/path}, respecting the Servlet context root, {@literal