Makefile: Create bin directory if it doesn't exist

Makefile

@@ -1,8 +1,9 @@
 dev: rnnoise
-	mkdir bin/
+	mkdir -p bin/
 	go generate
 	go build -o bin/noisetorch
 release: rnnoise
+	mkdir -p bin/
 	go generate
 	CGO_ENABLED=0 GOOS=linux go build -a -ldflags '-s -w -extldflags "-static"' .
 	upx noisetorch
@@ -13,3 +14,4 @@ rnnoise:
 	cd librnnoise_ladspa/; \
 	cmake . -DBUILD_VST_PLUGIN=OFF -DBUILD_LV2_PLUGIN=OFF -DBUILD_LADSPA_PLUGIN=ON; \
 	make
+