Update sinatra

Author: cbothner

Gemfile.lock

@@ -206,7 +206,7 @@ GEM
     rack (2.0.5)
     rack-cache (1.7.1)
       rack (>= 0.4)
-    rack-protection (2.0.0)
+    rack-protection (2.0.4)
       rack
     rack-proxy (0.6.2)
       rack
@@ -322,10 +322,10 @@ GEM
       json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.2)
-    sinatra (2.0.0)
+    sinatra (2.0.4)
       mustermann (~> 1.0)
       rack (~> 2.0)
-      rack-protection (= 2.0.0)
+      rack-protection (= 2.0.4)
       tilt (~> 2.0)
     spring (2.0.2)
       activesupport (>= 4.2)