Update to Skia version m67

Aseprite can be compiled with m62, m65, and m67 now.
It looks like the Skia API is more stable now.

Discussions:
https://community.aseprite.org/t/compiling-aseprite-on-macos-high-sierra-10-13-4/1290/6
https://community.aseprite.org/t/error-with-compile-skia-mac-os/1267/8

INSTALL.md

@@ -234,7 +234,7 @@ Skia.
 
 You can always check the
 [official Skia instructions](https://skia.org/user/build) and select
-the OS you are building for. Aseprite uses the `aseprite-m62` Skia
+the OS you are building for. Aseprite uses the `aseprite-m67` Skia
 branch from `https://github.com/aseprite/skia`.
 
 ## Skia on Windows
@@ -266,7 +266,7 @@ Just ignore it.)
     cd C:\deps
     git clone https://github.com/aseprite/skia.git
     cd skia
-    git checkout aseprite-m62
+    git checkout aseprite-m67
     python tools/git-sync-deps
 
 (The `tools/git-sync-deps` will take some minutes because it downloads
@@ -299,7 +299,7 @@ several minutes to finish:
     git clone https://github.com/aseprite/skia.git
     export PATH="${PWD}/depot_tools:${PATH}"
     cd skia
-    git checkout aseprite-m62
+    git checkout aseprite-m67
     python tools/git-sync-deps
     gn gen out/Release --args="is_official_build=true skia_use_system_expat=false skia_use_system_icu=false skia_use_system_libjpeg_turbo=false skia_use_system_libpng=false skia_use_system_libwebp=false skia_use_system_zlib=false"
     ninja -C out/Release

src/she/skia/skia_surface.h

@@ -16,6 +16,7 @@
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkColorFilter.h"
+#include "SkColorPriv.h"
 #include "SkImageInfo.h"
 #include "SkRegion.h"
 #include "SkSurface.h"