Surrounded the removeObserver call with a try catch block.

[SudoPlz]

Fixes: #38

[codecov-io]

Codecov Report

Merging #39 into master will decrease coverage by 1.22%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #39      +/-   ##
==========================================
- Coverage   99.75%   98.53%   -1.23%     
==========================================
  Files           8        7       -1     
  Lines         414      409       -5     
  Branches       26       46      +20     
==========================================
- Hits          413      403      -10     
- Misses          1        4       +3     
- Partials        0        2       +2

Flag	Coverage Δ
#ios	98.28% <100%> (-0.98%)	⬇️
#osx	98.53% <100%> (-1.23%)	⬇️

Impacted Files	Coverage Δ
YLMoment/YLMomentObject.m	98.68% <100%> (-1.32%)	⬇️
YLMoment/YLMoment+Bundle.m	92% <0%> (-4%)	⬇️
YLMoment/YLMoment+RelativeTime.m	98.38% <0%> (-1.62%)	⬇️
YLMoment/YLMoment+Components.m	98.57% <0%> (-1.43%)	⬇️
YLMoment/YLMomentObject.h

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