use openssl instead of shasum

shasum is not on many platforms (like centos), use openssl instead.

scripts/get

@@ -95,7 +95,7 @@ downloadFile() {
 # installs it.
 installFile() {
   HELM_TMP="/tmp/$PROJECT_NAME"
-  local sum=$(shasum -a 256 ${HELM_TMP_FILE} | awk '{print $1}')
+  local sum=$(openssl sha -sha256 ${HELM_TMP_FILE} | awk '{print $2}')
   local expected_sum=$(cat ${HELM_SUM_FILE})
   if [ "$sum" != "$expected_sum" ]; then
     echo "SHA sum of $HELM_TMP does not match. Aborting."