fix: [abstract] Forces file to be read with utf8 encoding

[mokaddem]

Make PyMISP opens files in utf-8 and not the system default

[coveralls]

Coverage remained the same at 38.024% when pulling f965e57 on fix-force-utf8-on-read into c77603e on master.

[coveralls]

Coverage remained the same at 38.024% when pulling f965e57 on fix-force-utf8-on-read into c77603e on master.

[coveralls]

Coverage remained the same at 38.024% when pulling f965e57 on fix-force-utf8-on-read into c77603e on master.

[codecov]

Codecov Report

Merging #565 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #565   +/-   ##
=======================================
  Coverage   38.07%   38.07%           
=======================================
  Files          35       35           
  Lines        7068     7068           
=======================================
  Hits         2691     2691           
  Misses       4377     4377           

Impacted Files	Coverage Δ
pymisp/abstract.py	78.40% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c77603e...f965e57. Read the comment docs.