Update appveyor.yml

Author: pdimov

appveyor.yml

@@ -26,13 +26,13 @@ environment:
   - LIB: filesystem
     GENERATOR: MinGW Makefiles
     CMAKE_BUILD_TYPE: Debug
-    PATH: C:\mingw-w64\x86_64-7.2.0-posix-seh-rt_v5-rev1\mingw64\bin;%PATH%
+    PATH: C:\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin;%PATH%
     UBP: 1
     TOOLSET: gcc
   - LIB: filesystem
     GENERATOR: MinGW Makefiles
     CMAKE_BUILD_TYPE: RelWithDebInfo
-    PATH: C:\mingw-w64\x86_64-7.2.0-posix-seh-rt_v5-rev1\mingw64\bin;%PATH%
+    PATH: C:\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin;%PATH%
     UBP: 1
     TOOLSET: gcc
   - LIB: filesystem