use text instead of string for db columns

db/migrate/20170613154149_create_gpg_signatures.rb

@@ -13,8 +13,8 @@ class CreateGpgSignatures < ActiveRecord::Migration
       t.binary :commit_sha, limit: Gitlab::Database.mysql? ? 20 : nil
       t.binary :gpg_key_primary_keyid, limit: Gitlab::Database.mysql? ? 20 : nil
 
-      t.string :gpg_key_user_name
-      t.string :gpg_key_user_email
+      t.text :gpg_key_user_name
+      t.text :gpg_key_user_email
 
       t.index :commit_sha
       t.index :gpg_key_primary_keyid

db/schema.rb

@@ -560,8 +560,8 @@ ActiveRecord::Schema.define(version: 20170725145659) do
     t.boolean "valid_signature"
     t.binary "commit_sha"
     t.binary "gpg_key_primary_keyid"
-    t.string "gpg_key_user_name"
-    t.string "gpg_key_user_email"
+    t.text "gpg_key_user_name"
+    t.text "gpg_key_user_email"
   end
 
   add_index "gpg_signatures", ["commit_sha"], name: "index_gpg_signatures_on_commit_sha", using: :btree