Revert updating prism in typecheck

Author: k0kubun

gemfiles/typecheck/Gemfile.lock

@@ -43,7 +43,7 @@ GEM
       ast (~> 2.4.1)
       racc
     power_assert (3.0.1)
-    prism (1.8.0)
+    prism (1.7.0)
     racc (1.8.1)
     rainbow (3.1.1)
     rake (13.3.1)