refactor: use _HANDLER variable instead of HANDLER in the bootstrap

Author: skunxicat

runtime/bootstrap

@@ -6,7 +6,7 @@
 set -eo pipefail
 
 # Initialization - load function handler
-source $LAMBDA_TASK_ROOT/"$(echo $HANDLER | cut -d. -f1).sh"
+source $LAMBDA_TASK_ROOT/"$(echo $_HANDLER | cut -d. -f1).sh"
 
 # Processing
 while true