Fix some typos in various files

Issue/feature addressed

Just correcting some typos in the comment section of few files

Proposed solution

Implementation

Tests

Notes

Please add any other information that could be useful for reviewers.

Checklist

• [x] Functions and classes, or changes to them, are documented.
• [x] User guide/documentation is updated.
• [x] Changelog is updated.
• [x] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines). -~~ [x] License added to any new files.~~
• [x] No extraneous files have been added (e.g. compiler output or test data files).

Warning

On the 19.07 the code formatting (code style) was standardised using clang-format, over the whole Nektar++ code. This means changes in your branch will conflict with formatting changes on the master branch. To resolve these conflicts , see #295 (closed)