fixed the output given when username is taken

[tatougueye]

I fixed the output given if username is taken when registering in NodeBB from 'Username taken' to 'Username taken. Maybe try [username]suffix'. resolves #1

[coveralls]

Pull Request Test Coverage Report for Build 10834482797

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.005%) to 82.666%

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Files with Coverage Reduction	New Missed Lines	%
src/meta/errors.js	1	76.74%

Totals
Change from base Build 10805636900:	-0.005%
Covered Lines:	22322
Relevant Lines:	25582

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💛 - Coveralls