Fixing casing sqlContext and transactionContext

This was a problem on Ubuntu. `index.js` was requiring those files by `sqlContext` and `transactionContext`, but they files were names `SqlContext` and `TransactionContext`. Node was throwing an error saying the file could not be found. 

On other platforms that are not case-sensitive (like Windows) this was a non-issue. 

Adjusting the case of the files solved the problem.