Add graceful degradation for sha_cmd in get.sh

The earlier choice of using shasum was made for broadest support reasons.  However
the breadth of support could be broader still by introducing graceful degradation
to get.sh.  This change defaults the command to be used to sha256sum and reverts to
shasum -a 256 if the default isnt found.

Signed-off-by: Richard Gee <richard@technologee.co.uk>

Author: rgee0

get.sh

@@ -30,12 +30,20 @@ hasCli() {
     fi
 }
 
+
 checkHash(){
-    if [ -x "$(command -v shasum)" ]; then
+
+    sha_cmd="sha256sum"
+
+    if [ ! -x "$(command -v $sha_cmd)" ]; then
+    sha_cmd="shasum -a 256"
+    fi
+
+    if [ -x "$(command -v $sha_cmd)" ]; then
 
     targetFileDir=${targetFile%/*}
 
-    (cd $targetFileDir && curl -sSL $url.sha256|shasum -c -s)
+    (cd $targetFileDir && curl -sSL $url.sha256|$sha_cmd -c -s)
 
         if [ "$?" != "0" ]; then
             rm $targetFile
@@ -108,7 +116,7 @@ getPackage() {
         else
 
             echo
-            echo "Running as root - Attemping to move faas-cli to /usr/local/bin"
+            echo "Running as root - Attempting to move faas-cli to /usr/local/bin"
 
             mv $targetFile /usr/local/bin/faas-cli