Unlock thor again

It looks like all commands we use in production fixed the warnings
(rails 5.1), so we can update that again.

Gemfile

@@ -206,12 +206,6 @@ gem "minitest"
 
 gem "versionist", "1.6.0"
 
-# Prevent accidental upgrades of thor
-# TODO: remove this when either all gems depending on thor have fixed the warnings
-#       or thor released a version where they are clearly marked as warnings
-# see: https://github.com/erikhuda/thor/issues/538
-gem "thor", "0.19.1"
-
 # Windows and OSX have an execjs compatible runtime built-in, Linux users should
 # install Node.js or use "therubyracer".
 #

Gemfile.lock

@@ -690,7 +690,7 @@ GEM
       tins (~> 1.0)
     terminal-table (1.8.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
-    thor (0.19.1)
+    thor (0.19.4)
     thread_safe (0.3.6)
     tilt (2.0.8)
     timecop (0.9.1)
@@ -890,7 +890,6 @@ DEPENDENCIES
   spring-commands-rspec (= 1.0.4)
   sprockets-rails (= 3.2.0)
   string-direction (= 1.2.0)
-  thor (= 0.19.1)
   timecop (= 0.9.1)
   turbo_dev_assets (= 0.0.2)
   twitter (= 6.1.0)