Update Kemal to 0.21.0 (#2959)

frameworks/Crystal/kemal/.gitignore

@@ -1,4 +1,5 @@
 libs/
+lib/
 .crystal
 .shards
 !shard.lock

frameworks/Crystal/kemal/shard.lock

@@ -6,11 +6,11 @@ shards:
 
   kemal:
     github: sdogruyol/kemal
-    version: 0.19.0
+    version: 0.21.0
 
   kilt:
     github: jeromegn/kilt
-    version: 0.3.3
+    version: 0.4.0
 
   pg:
     github: will/crystal-pg

frameworks/Crystal/kemal/shard.yml

@@ -7,7 +7,7 @@ dependencies:
     version: "0.13.3"
   kemal:
     github: "sdogruyol/kemal"
-    version: "0.19.0"
+    version: "0.21.0"
   redis:
     github: "stefanwille/crystal-redis"
     version: "1.8.0"