KeywordCipher:
* Fixed a typing mistake

SubstitutionCipher:
- Removed unnecessary imports

TestKeywordCipher:
+ Added @SuppressWarnings annotation

TestShiftCipher:
- Removed unneccesary import
+ Added @SuppressWarnings annotation

TestMonoalphabeticCipher:
+ Added comments

TestSubstitutionCipher:
+ Added comments
Merge remote-tracking branch 'origin/master'