docs(license): update license year to 2018

[fulls1z3]

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

• [x] The commit message follows our guidelines: https://github.com/fulls1z3/ngx-i18n-router/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
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] 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?

[ ] Yes
[x] No

** Other information

[codecov[bot]]

Codecov Report

Merging #108 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #108   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files           5        5           
  Lines         162      162           
  Branches       47       47           
=======================================
  Hits          161      161           
  Misses          1        1

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