[ruby/webrick] Remove the squishing of whitespace in header values

While the stripping of header values is required by RFC 2616 4.2 and
RFC 7230 3.2.4, the squishing is not and can break things, such as
when one header contains an HMAC of another header.

Fixes Ruby Bug 7021.

https://github.com/ruby/webrick/commit/8b96088a86

lib/webrick/httputils.rb

@@ -162,10 +162,7 @@ module WEBrick
         end
       }
       header.each{|key, values|
-        values.each{|value|
-          value.strip!
-          value.gsub!(/\s+/, " ")
-        }
+        values.each(&:strip!)
       }
       header
     end

test/webrick/test_httprequest.rb

@@ -135,7 +135,7 @@ GET /
     assert_equal("", req.script_name)
     assert_equal("/foo/baz", req.path_info)
     assert_equal("9", req['content-length'])
-    assert_equal("FOO BAR BAZ", req['user-agent'])
+    assert_equal("FOO   BAR BAZ", req['user-agent'])
     assert_equal("hogehoge\n", req.body)
   end