refactor: change double to single quotes

[GreenTeaCake]

Change double to single quotes to match current tslint settings.

[codecov-io]

Codecov Report

Merging #146 into master will not change coverage. The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #146   +/-   ##
=======================================
  Coverage   88.46%   88.46%           
=======================================
  Files           7        7           
  Lines          78       78           
  Branches        7        7           
=======================================
  Hits           69       69           
  Misses          6        6           
  Partials        3        3

Impacted Files	Coverage Δ
src/app/toolbar/toolbar.module.ts	100% <100%> (ø)	:arrow_up:
src/app/toolbar/toolbar.component.ts	85.71% <100%> (ø)	:arrow_up:
src/app/shared.module.ts	100% <100%> (ø)	:arrow_up:
src/app/app.component.ts	100% <100%> (ø)	:arrow_up:

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[btroncone]

lgtm 👍