Update Syria and Mauritania flags

[simoheinonen]

These two seem outdated

https://github.com/rinvex/countries/blob/master/resources/flags/mr.svg
https://github.com/rinvex/countries/blob/master/resources/flags/sy.svg

https://en.wikipedia.org/wiki/Flag_of_Mauritania
https://en.wikipedia.org/wiki/Flag_of_Syria