HBASE-19770 ADDENDUM Replace `if not` with `unless`

Signed-off-by: Mike Drob <mdrob@apache.org>

hbase-shell/src/main/ruby/shell.rb

@@ -83,7 +83,7 @@ module Shell
       self.interactive = interactive
       self.return_values = return_values
       # If we're in non-interactive mode, force return_values
-      self.return_values = true if not self.interactive
+      self.return_values = true unless self.interactive
     end
 
     # Returns Admin class from admin.rb