Upgraded rack-test gem

Author: jasnow

Gemfile.lock

@@ -201,7 +201,7 @@ GEM
     rack (2.0.4)
     rack-livereload (0.3.16)
       rack
-    rack-test (0.8.2)
+    rack-test (0.8.3)
       rack (>= 1.0, < 3)
     rails (5.1.5)
       actioncable (= 5.1.5)