conditionally append .exe to windows only builds

Makefile

@@ -1,12 +1,22 @@
 .ONESHELL:
 .PHONY: web app all
 
+FILENAME =
+
+ifdef OS
+	# Windows (%OS% env variable only exists on Windows)
+	FILENAME = logstation.exe
+else
+	# Unix-like OS (Linux, Mac/OSX, BSD, etc)
+	FILENAME = logstation
+endif
+
 all:
 	$(MAKE) web
 	$(MAKE) app
 
 app:
-	go build -o logstation ./main.go
+	go build -o ${FILENAME} ./main.go
 
 web:
 	cd web && npm run build