feat: upgrade to angular 5

[fulls1z3]

** PR Checklist
Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/fulls1z3/ngx-translate/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

** PR Type
What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[x] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] Other... Please describe:

** What is the current behavior?

Issue Number: N/A

** What is the new behavior?

** Does this PR introduce a breaking change?

[x] Yes
[ ] No

** Other information