snap: Make it build with Go 1.18

snap/snapcraft.yaml

@@ -47,8 +47,8 @@ parts:
       export GOPATH=$(realpath ../go)
       export PATH=$GOPATH/bin:$PATH
 
-      echo ' * Running "go get -v github.com/magefile/mage"...'
-      go get -v github.com/magefile/mage
+      echo ' * Running "go install -v github.com/magefile/mage"...'
+      go install -v github.com/magefile/mage
 
       #echo ' * Running "mage -v test"...'
       #mage -v test