helpers: Don't clean path twice
helpers: Don't clean path twice

Join calls Clean as it says in docs.

Minor performance improvement:
Before:
Average time per operation: 432ms
Average memory allocated per operation: 127322kB
Average allocations per operation: 2138137

After:
Average time per operation: 428ms
Average memory allocated per operation: 127350kB
Average allocations per operation: 2137892

digitalcraftsman/hugo,mitchchn/hugo,gohugoio/hugo,anthonyfok/hugo,anthonyfok/hugo,mdhender/hugo,gohugoio/hugo,anthonyfok/hugo,fedelibre/hugo,mdhender/hugo,fedelibre/hugo,fedelibre/hugo,gohugoio/hugo,digitalcraftsman/hugo,mitchchn/hugo,mdhender/hugo,mdhender/hugo,fedelibre/hugo