lib: concatenated stirng to template string

[pajangid]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

When I ran the test got the following error message, looks like unrelated to the PR

/usr/bin/python2.7 tools/test.py --mode=release -J \
        async-hooks \
        default \
        addons addons-napi \
        doctool \
        known_issues
=== release test-async-wrap-uncaughtexception ===
Path: parallel/test-async-wrap-uncaughtexception
Mismatched <anonymous> function calls. Expected exactly 1, actual 2.
    at Object.exports.mustCall (/home/k.vijayalakshmi/pawan/node/test/common/index.js:490:10)
    at Object.<anonymous> (/home/k.vijayalakshmi/pawan/node/test/parallel/test-async-wrap-uncaughtexception.js:14:33)
    at Module._compile (module.js:641:30)
    at Object.Module._extensions..js (module.js:652:10)
    at Module.load (module.js:560:32)
    at tryModuleLoad (module.js:503:12)
    at Function.Module._load (module.js:495:3)
    at Function.Module.runMain (module.js:682:10)
    at startup (bootstrap_node.js:191:16)
Command: out/Release/node /home/k.vijayalakshmi/pawan/node/test/parallel/test-async-wrap-uncaughtexception.js
[02:33|% 100|+ 2068|-   1]: Done
Makefile:213: recipe for target 'test' failed
make: *** [test] Error 1

Submitting my first PR for node.js, please have a look

[fhinkel]

CI: https://ci.nodejs.org/job/node-test-pull-request/11359/

[fhinkel]

@pajangid Thanks so much for your first commit 🎉. Landed as 23afa30

[MylesBorins]

I've opted to not land this on v6.x as I am unsure if interpolated strings are optimized with that version of V8