set mingw gcc to version 8

.ci/conan_profile_mingw_gcc8.1 → .ci/conan_profile_mingw_gcc8

@@ -5,7 +5,7 @@ os_build=Windows
 arch=x86_64
 arch_build=x86_64
 compiler=gcc
-compiler.version=8.1
+compiler.version=8
 compiler.exception=seh
 compiler.libcxx=libstdc++11
 compiler.threads=posix