Wrap up loose ends from PR review

[wvdtoorn]

Fixes #2537

Changes made in this Pull Request:

• Two small formatting and grammar fixes

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

[codecov]

Codecov Report

Merging #2633 into densityanalysis-2502 will increase coverage by 0.83%.
The diff coverage is n/a.

@@                   Coverage Diff                    @@
##           densityanalysis-2502    #2633      +/-   ##
========================================================
+ Coverage                 91.01%   91.85%   +0.83%     
========================================================
  Files                       174       15     -159     
  Lines                     23601     2013   -21588     
  Branches                   3075        0    -3075     
========================================================
- Hits                      21480     1849   -19631     
+ Misses                     1498      164    -1334     
+ Partials                    623        0     -623

Impacted Files	Coverage Δ
package/MDAnalysis/coordinates/GRO.py
package/MDAnalysis/coordinates/base.py
package/MDAnalysis/analysis/helanal.py
package/MDAnalysis/topology/MinimalParser.py
package/MDAnalysis/visualization/__init__.py
...e/MDAnalysis/analysis/encore/clustering/cluster.py
package/MDAnalysis/coordinates/DCD.py
package/MDAnalysis/coordinates/GSD.py
package/MDAnalysis/coordinates/memory.py
package/MDAnalysis/exceptions.py
... and 148 more

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