Switched to the latest at present stable Mono (4.2.1) for the OS X build.
Switched to the latest at present stable Mono (4.2.1) for the OS X build.

We used to rely on the latest nightly build because it used to have the same name but this is no longer true.

Signed-off-by: Dimitar Dobrev <ca751a5c976abad79158718440750fc638d19ebc@protonmail.com>

mohtamohit/CppSharp,zillemarco/CppSharp,genuinelucifer/CppSharp,mohtamohit/CppSharp,zillemarco/CppSharp,u255436/CppSharp,ktopouzi/CppSharp,ddobrev/CppSharp,inordertotest/CppSharp,zillemarco/CppSharp,zillemarco/CppSharp,u255436/CppSharp,genuinelucifer/CppSharp,u255436/CppSharp,mono/CppSharp,u255436/CppSharp,inordertotest/CppSharp,ktopouzi/CppSharp,genuinelucifer/CppSharp,inordertotest/CppSharp,inordertotest/CppSharp,u255436/CppSharp,mohtamohit/CppSharp,genuinelucifer/CppSharp,ddobrev/CppSharp,mohtamohit/CppSharp,mono/CppSharp,inordertotest/CppSharp,ddobrev/CppSharp,mono/CppSharp,genuinelucifer/CppSharp,ddobrev/CppSharp,zillemarco/CppSharp,mohtamohit/CppSharp,mono/CppSharp,ktopouzi/CppSharp,ktopouzi/CppSharp,mono/CppSharp,ddobrev/CppSharp,ktopouzi/CppSharp,mono/CppSharp