docs(Auth-with-Ionic3-Angular4) Fix Typos

[nicolaslwilson]

Fixes some minor spelling errors, makes punctuation more consistent throughout.

Checklist

• Issue number for this PR: n/a
• Docs included?: yes (is a doc update)
• Test units included?: none affected
• e2e tests included?: none affected
• In a clean directory, npm install, npm run build, and npm test run successfully? n/a

Description
Fixes some minor spelling errors, makes punctuation more consistent throughout.

Code sample
n/a

[davideast]

Thanks @nicolaslwilson!