appveyor: try installing zstd
diff --git a/appveyor.yml b/appveyor.yml
index 290a0af..21d6456 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -56,7 +56,7 @@
 
 before_build:
   cmd: >-
-    vcpkg install zlib:%TRIPLET% bzip2:%TRIPLET% liblzma:%TRIPLET%
+    vcpkg install zlib:%TRIPLET% bzip2:%TRIPLET% liblzma:%TRIPLET% zstd:%TRIPLET%
 
     mkdir build