Add space after description if needed

[IanButterworth]

Currently the desc is required to have a trailing space, otherwise you end up with

Custom message100%|█████████████████████| Time: 0:00:00

This just checks if there is a trailing space and adds one if not.
Intended to be the minimal way to fix this.

[codecov]

Codecov Report

Merging #233 (86edd6c) into master (5826a75) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #233      +/-   ##
==========================================
+ Coverage   96.31%   96.32%   +0.01%     
==========================================
  Files           1        1              
  Lines         515      517       +2     
==========================================
+ Hits          496      498       +2     
  Misses         19       19              

Impacted Files	Coverage Δ
src/ProgressMeter.jl	96.32% <100.00%> (+0.01%)	⬆️

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