UpdateClass::setMD5 store expected md5 in lowercase (espressif#8959)

* set _target_md5 to lowercase

* fix errors

Author: P-R-O-C-H-Y

libraries/Update/src/Updater.cpp

@@ -278,6 +278,7 @@ bool UpdateClass::setMD5(const char * expected_md5){
         return false;
     }
     _target_md5 = expected_md5;
+    _target_md5.toLowerCase();
     return true;
 }