fix: update gems and locks

Author: jdalton

Gemfile.lock

@@ -21,7 +21,7 @@ GEM
     execjs (2.7.0)
     faraday (0.14.0)
       multipart-post (>= 1.2, < 3)
-    ffi (1.9.18)
+    ffi (1.16.0)
     forwardable-extended (2.6.0)
     gemoji (3.0.0)
     github-pages (175)
@@ -192,7 +192,7 @@ GEM
       rb-fsevent (>= 0.9.3)
       rb-inotify (>= 0.9.7)
     mercenary (0.3.6)
-    mimemagic (0.3.2)
+    mimemagic (0.3.7)
     mini_portile2 (2.3.0)
     minima (2.1.1)
       jekyll (~> 3.3)