Fix grammar errors

[qmoya]

“Enter user name?”, with a question mark, is a question to which the answer is either “yes” or “no,” not a username. Accordingly, I removed the question mark. (Another possibility would be to simply ask: “What’s your username?”)

Also, the Oxford Dictionary of English gives the compound word “username” to refer to "an identification used by a person with access to a computer, network, or online service,” which I suppose it’s the meaning intended here. I rewrote it like that.

[codecov-io]

Codecov Report

Merging #41 into master will decrease coverage by 2.33%. The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #41      +/-   ##
=========================================
- Coverage   98.93%   96.6%   -2.34%     
=========================================
  Files          11      39      +28     
  Lines         936    1912     +976     
  Branches        0      63      +63     
=========================================
+ Hits          926    1847     +921     
- Misses         10      65      +55

Impacted Files	Coverage Δ
SwiftlineTests/SwiftlineTests/ArgsTests.swift	100% <0%> (ø)	:arrow_up:
SwiftlineTests/SwiftlineTests/ColorizerTest.swift	100% <0%> (ø)	:arrow_up:
SwiftlineTests/SwiftlineTests/AgreeTests.swift	100% <0%> (ø)	:arrow_up:
SwiftlineTests/SwiftlineTests/GlobTests.swift	100% <0%> (ø)	:arrow_up:
...iftlineTests/SwiftlineTests/AskSettingsTests.swift	100% <0%> (ø)	:arrow_up:
SwiftlineTests/SwiftlineTests/RunnerTests.swift	100% <0%> (ø)	:arrow_up:
SwiftlineTests/SwiftlineTests/ENVTests.swift	100% <0%> (ø)	:arrow_up:
SwiftlineTests/SwiftlineTests/AskTests.swift	100% <0%> (ø)	:arrow_up:
...ftlineTests/SwiftlineTests/AgreeSettingsTest.swift	100% <0%> (ø)	:arrow_up:
Source/Glob.swift	100% <0%> (ø)
... and 29 more

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