Maintenance: Update dependency net-ftp to v0.3.8

Gemfile.lock

@@ -370,7 +370,7 @@ GEM
     mysql2 (0.5.6)
     naught (1.1.0)
     nestful (1.1.4)
-    net-ftp (0.3.7)
+    net-ftp (0.3.8)
       net-protocol
       time
     net-http (0.4.1)