install_gradle: Use curl instead of wget
install_gradle: Use curl instead of wget

wget is not available by default in the MSYS2 environment AppVeyor is
running.

In the same run, download only the "-bin" Gradle distribution to safe some
download time.

tinfoil/LicenseFinder,bdshroyer/LicenseFinder,tinfoil/LicenseFinder,sschuberth/LicenseFinder,sschuberth/LicenseFinder,pivotal/LicenseFinder,sschuberth/LicenseFinder,bdshroyer/LicenseFinder,tinfoil/LicenseFinder,joemoore/LicenseFinder,pivotal/LicenseFinder,bdshroyer/LicenseFinder,joemoore/LicenseFinder,joemoore/LicenseFinder,pivotal/LicenseFinder,bspeck/LicenseFinder,joemoore/LicenseFinder,bdshroyer/LicenseFinder,pivotal/LicenseFinder,pivotal/LicenseFinder,tinfoil/LicenseFinder,bdshroyer/LicenseFinder,pivotal/LicenseFinder,bspeck/LicenseFinder,sschuberth/LicenseFinder,bspeck/LicenseFinder,tinfoil/LicenseFinder,pivotal/LicenseFinder,joemoore/LicenseFinder,bspeck/LicenseFinder,bspeck/LicenseFinder,sschuberth/LicenseFinder