Fix UF2 converter error on docker environment

Author: sekigon-gonnoc

util/docker_build.sh

@@ -36,7 +36,7 @@ if [ -z "$RUNTIME" ]; then
 		exit 2
 	fi
 fi
-	
+
 
 # Determine arguments
 if [ $# -eq 0 ]; then
@@ -81,5 +81,6 @@ fi
 	-e ALT_GET_KEYBOARDS=true \
 	-e SKIP_GIT="$SKIP_GIT" \
 	-e MAKEFLAGS="$MAKEFLAGS" \
+	-e USER="" \
 	qmkfm/base_container \
 	make "$keyboard${keymap:+:$keymap}${target:+:$target}"