Merge pull request #748 from Shopify/work_around_rvm_fd_9_issue

Gracefully ignore ArgumentError in the shim check

lib/shopify-cli/core/entry_point.rb

@@ -11,6 +11,12 @@ def call(args, ctx = Context.new)
             IO.open(9) { is_shell_shim = true }
           rescue Errno::EBADF
             # This is expected if the descriptor doesn't exist
+          rescue ArgumentError => e
+            # This can happen on RVM, because it can use fd 9 itself and block access to it. That only happens if the fd
+            # did not exist beforehand, so that means there was no fd 9 before Ruby started.
+            unless e.message == 'The given fd is not accessible because RubyVM reserves it'
+              raise e
+            end
           end
 
           if !ctx.testing? && is_shell_shim