Fix spec_request on ruby-trunk (2.2.0dev)

Manually percent-encode square brackets in query string. This fixes
current travis build issues.

2.2.0dev has recently changed URI parsing from RFC2396 to RFC3986.
Square brackets in RFC3986 are required to be percent-encoded when
present in the query string of a URI. URI.encode on 2.2.0dev isn't
currently updated to support this encoding (see:
    https://bugs.ruby-lang.org/issues/9990)
Merge pull request #708 from lengarvey/fix_uri_encoding_ruby_220_rfc3986

Fix spec_request on ruby-trunk (2.2.0dev)