Maintenance: Updated mimemagic gem dependency to 0.3.6.

Gem got deprecated and version 0.3.5 was yanked. 0.3.6 only introduced a licensing change.

Gemfile.lock

@@ -287,7 +287,7 @@ GEM
     mime-types (3.2.2)
       mime-types-data (~> 3.2015)
     mime-types-data (3.2019.0331)
-    mimemagic (0.3.5)
+    mimemagic (0.3.6)
     mini_mime (1.0.2)
     mini_portile2 (2.5.0)
     mini_racer (0.2.9)