Ignore the output of ch.ShowChart() in the fsx helper files

This is to avoid the following error:

warning FS0020: This expression should have type 'unit', but has type 'Windows.Forms.Form'. Use 'ignore' to discard the result of the expression, or 'let' to bind the result to a name.
Merge pull request #51 from MattButton/master

Ignore the output of ch.ShowChart() in the fsx helper files