Update parallel_multiengine.rst

Using :meth: apparently adds parens, so in this example, the generated text in the help page looks like:

view.execute('import numpy')()

which is incorrect (note extra parens at end). Not sure what this should be, other than just marked as code.

![screenshot from 2014-12-30 09 24 22](https://cloud.githubusercontent.com/assets/168568/5579356/114b8e06-9007-11e4-936d-a23627fd9d4e.png)