propagate the error properly to tailor errors [fixes #178]

[vigneshshanmugam]

• Error was not rethrown before back to the fetchTemplate function
• Added a test case for the missing case.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@99ba67e). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #179   +/-   ##
=========================================
  Coverage          ?   96.79%           
=========================================
  Files             ?       14           
  Lines             ?      561           
  Branches          ?       94           
=========================================
  Hits              ?      543           
  Misses            ?       18           
  Partials          ?        0

Impacted Files	Coverage Δ
lib/fetch-template.js	100% <100%> (ø)

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[DeTeam]

👍

[vigneshshanmugam]

👍