update rack version

Gemfile.lock

@@ -66,11 +66,13 @@ GEM
     mustermann-grape (1.0.2)
       mustermann (>= 1.0.0)
     pg (1.4.5)
-    rack (2.0.5)
+    rack (1.6.13)
     rack-accept (0.4.5)
       rack (>= 0.4)
-    rack-cors (1.1.1)
-      rack (>= 2.0.0)
+    rack-cors (1.0.6)
+      rack (>= 1.6.0)
+    rack-protection (1.5.5)
+      rack
     rack-test (2.0.2)
       rack (>= 1.3)
     racksh (1.0.0)
@@ -87,9 +89,12 @@ GEM
     ruby2_keywords (0.0.5)
     shotgun (0.9.2)
       rack (>= 1.0)
-    sinatra (1.0)
-      rack (>= 1.0)
+    sinatra (1.4.8)
+      rack (~> 1.5)
+      rack-protection (~> 1.4)
+      tilt (>= 1.3, < 3)
     thread_safe (0.3.6)
+    tilt (2.0.11)
     tzinfo (1.2.11)
       thread_safe (~> 0.1)
     unicorn (4.8.3)
@@ -117,7 +122,7 @@ DEPENDENCIES
   minitest
   minitest-reporters
   pg
-  rack (= 2.0.5)
+  rack (= 1.6.13)
   rack-cors
   rack-test
   racksh (= 1.0.0)