Use ora as task loader and update the code

[alexcanessa]

Now using: ora as new task manager.

resolves #102

[codecov-io]

Codecov Report

Merging #107 into master will increase coverage by 0.86%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   85.47%   86.34%   +0.86%     
==========================================
  Files           7        7              
  Lines         303      293      -10     
==========================================
- Hits          259      253       -6     
+ Misses         44       40       -4

Impacted Files	Coverage Δ
lib/src/_utils.js	100% <100%> (ø)	⬆️
lib/src/Gren.js	85.47% <44.44%> (+1.26%)	⬆️

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