snap: Replace deprecated build and install keyword

These keywords has been obsoleted in Snapcraft 3.

Refer-to: The 'build' keyword has been replaced by 'override-build' <https://github.com/canonical-web-and-design/snappy-docs/blob/master/deprecation-notices/dn8.md>
Refer-to: The 'install' keyword has been replaced by 'override-build' <https://github.com/canonical-web-and-design/snappy-docs/blob/master/deprecation-notices/dn9.md>
Signed-off-by: 林博仁(Buo-ren Lin) <Buo.Ren.Lin@gmail.com>

snap/snapcraft.yaml

@@ -38,7 +38,7 @@ parts:
     build-packages:
       - cabal-install
       - squid3
-    build: |
+    override-build: |
       # See comments in .snapsquid.conf
       [ "$http_proxy" ] && {
         squid3 -f .snapsquid.conf
@@ -48,6 +48,6 @@ parts:
       cabal sandbox init
       cabal update || cat /var/log/squid/*
       cabal install -j
-    install: |
+
       install -d $SNAPCRAFT_PART_INSTALL/usr/bin
       install .cabal-sandbox/bin/shellcheck $SNAPCRAFT_PART_INSTALL/usr/bin