Use single brackets for portability with other shells

diff --git a/keyboards/lets_split/rules.mk b/keyboards/lets_split/rules.mk
index 79860ea35d5cbd9b1613812c7326e180afaa1d20..43eff99e71c2d37944f785548722e09c4c98aa29 100644 (file)
--- a/keyboards/lets_split/rules.mk
+++ b/keyboards/lets_split/rules.mk
@@ -78,7 +78,7 @@ CUSTOM_MATRIX = yes
 avrdude: build
        ls /dev/tty* > /tmp/1; \
        echo "Reset your Pro Micro now"; \
-       while [[ -z $$USB ]]; do \
+       while [ -z $$USB ]; do \
          sleep 1; \
          ls /dev/tty* > /tmp/2; \
          USB=`diff /tmp/1 /tmp/2 | grep -o '/dev/tty.*'`; \