Bump sinatra, rack and koala

Gemfile

@@ -5,4 +5,4 @@ gem "koala"
 gem "json", "1.5.5"
 gem "httparty"
 gem "thin"
-gem "rack", "1.3.10"
+gem "rack", "3.1.8"

Gemfile.lock

@@ -1,31 +1,49 @@
 GEM
   remote: http://rubygems.org/
   specs:
-    addressable (2.2.7)
+    addressable (2.8.7)
+      public_suffix (>= 2.0.2, < 7.0)
+    base64 (0.2.0)
     crack (0.1.8)
     daemons (1.1.3)
     eventmachine (0.12.10)
-    faraday (0.7.6)
-      addressable (~> 2.2)
-      multipart-post (~> 1.1)
-      rack (~> 1.1)
+    faraday (2.12.0)
+      faraday-net_http (>= 2.0, < 3.4)
+      json
+      logger
+    faraday-net_http (3.3.0)
+      net-http
     httparty (0.7.8)
       crack (= 0.1.8)
     json (1.5.5)
-    koala (1.3.0)
-      faraday (~> 0.7.0)
-      multi_json (~> 1.0)
-    multi_json (1.0.3)
-    multipart-post (1.1.5)
-    rack (1.3.10)
-    sinatra (1.2.6)
-      rack (~> 1.1)
-      tilt (>= 1.2.2, < 2.0)
+    koala (2.5.0)
+      addressable
+      faraday
+    logger (1.6.1)
+    mustermann (3.0.3)
+      ruby2_keywords (~> 0.0.1)
+    net-http (0.4.1)
+      uri
+    public_suffix (6.0.1)
+    rack (3.1.8)
+    rack-protection (4.0.0)
+      base64 (>= 0.1.0)
+      rack (>= 3.0.0, < 4)
+    rack-session (2.0.0)
+      rack (>= 3.0.0)
+    ruby2_keywords (0.0.5)
+    sinatra (4.0.0)
+      mustermann (~> 3.0)
+      rack (>= 3.0.0, < 4)
+      rack-protection (= 4.0.0)
+      rack-session (>= 2.0.0, < 3)
+      tilt (~> 2.0)
     thin (1.2.11)
       daemons (>= 1.0.9)
       eventmachine (>= 0.12.6)
       rack (>= 1.0.0)
-    tilt (1.3.3)
+    tilt (2.4.0)
+    uri (0.13.1)
 
 PLATFORMS
   ruby
@@ -34,6 +52,6 @@ DEPENDENCIES
   httparty
   json (= 1.5.5)
   koala
-  rack (= 1.3.10)
+  rack (= 3.1.8)
   sinatra
   thin