arm64 on darwin is available for go1.16 or newer

Fixes the error message that is printed
if you request Go < 1.16 on darwin/arm64.

gimme

@@ -916,9 +916,14 @@ case "${GIMME_ARCH}" in
 x86_64) GIMME_ARCH=amd64 ;;
 x86) GIMME_ARCH=386 ;;
 arm64)
-	if [[ "${GIMME_GO_VERSION}" != master && "$(_versint "${GIMME_GO_VERSION}")" < "$(_versint 1.5)" ]]; then
+	min_arm64_version=1.5
+	if [[ "${GIMME_HOSTOS}" == 'darwin' ]]; then
+		min_arm64_version=1.16
+	fi
+
+	if [[ "${GIMME_GO_VERSION}" != master && "$(_versint "${GIMME_GO_VERSION}")" < "$(_versint "$min_arm64_version")" ]]; then
 		echo >&2 "error: ${GIMME_ARCH} is not supported by this go version"
-		echo >&2 "try go1.5 or newer"
+		echo >&2 "try go${min_arm64_version} or newer"
 		exit 1
 	fi
 	if [[ "${GIMME_HOSTOS}" == "linux" && "${GIMME_HOSTARCH}" != "${GIMME_ARCH}" ]]; then