Change installation link in exercise READMEs

[tejasbubane]

Each exercise has a README file with a setup link in it.

The link points to http://exercism.io/languages/ecmascript/ but the setup instructions are in http://exercism.io/languages/ecmascript/installation.

Task: Change the link to the correct installation link in README files of all exercises.

[lantran]

I would like to work on this issue.

[tejasbubane]

@lantran Go for it!

[lantran]

PR submitted.