[rosalind] fix whitespace issue in mrna example
[rosalind] fix whitespace issue in mrna example

stmuk/perl6-examples,stmuk/perl6-examples,perl6/perl6-examples,Quinny/perl6-examples,Quinny/perl6-examples,shlomif/perl6-examples,perl6/perl6-examples,stmuk/perl6-examples,perl6/perl6-examples,perl6/perl6-examples,stmuk/perl6-examples,perl6/perl6-examples,shlomif/perl6-examples,shlomif/perl6-examples,shlomif/perl6-examples,Quinny/perl6-examples,stmuk/perl6-examples,shlomif/perl6-examples,Quinny/perl6-examples,Quinny/perl6-examples