Update known_good.json

Updated MoltenVK to 1.1.8

Author: richard-lunarg

scripts/known_good.json

@@ -14,7 +14,7 @@
  "sub_dir" : "MoltenVK",
  "build_dir" : "MoltenVK",
  "install_dir" : "MoltenVK",
- "commit" : "v1.1.7",
+ "commit" : "v1.1.8",
  "custom_build" : [
  "./fetchDependencies --macos --no-parallel-build",
  "xcodebuild -project MoltenVKPackaging.xcodeproj GCC_PREPROCESSOR_DEFINITIONS='$GCC_PREPROCESSOR_DEFINITIONS MVK_CONFIG_LOG_LEVEL=1' -scheme \"MoltenVK Package (macOS only)\" build"