fixes header padding error when first column is RightJustified

[vmogilev]

Prior to this fix, if the first table column is RightJustified, then tabular would loose the left padding on the header. Now, it works as expected and there is a test for this.

[codecov]

Codecov Report

Merging #2 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #2   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          28     31    +3     
=====================================
+ Hits           28     31    +3

Impacted Files	Coverage Δ
tabular.go	100% <100%> (ø)	⬆️

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