mantle: Remove now depreacted '-i' build flag
Fixes:
```
go build: -i flag is deprecated
go test: -i flag is deprecated
```
@@ -25,7 +25,7 @@ pkgs=$(go list -mod=vendor $PKG | grep -v /vendor/)
src=$(find . -name '*.go' -not -path "./vendor/*")
echo "Building tests..."
-go test -mod=vendor -i "$@" $pkgs
+go test -mod=vendor "$@" $pkgs
go install -mod=vendor $pkgs
echo "Running tests..."
