[BUG] Typo: This is a multiobjective "algortihm"

[jschueller]

This typo "algortihm" is found in several classes, eg https://github.com/esa/pagmo2/blob/master/src/algorithms/nsga2.cpp#L120

[bluescarni]

@jschueller Thanks for reporting, I'll make sure to fix the typos in the next version.

[bluescarni]

I think this was fixed in #518 , please re-open if needed.

[jschueller]

thanks