Typo in Table Name in SQL Statements in Migration File Example

[taeyang91]

Hey there! First off, thanks for all the hard work on this awesome gem. I came across a small typos in the migration file example. The table name in the SQL statements should be plural (pictures instead of picture).

• https://github.com/clio/polymorphic_integer_type/blob/master/README.md?plain=1#L103
• https://github.com/clio/polymorphic_integer_type/blob/master/README.md?plain=1#L122

Thanks again for maintaining this gem!