added directory creation

Author: squix78

.travis.yml

@@ -12,6 +12,7 @@ install:
 - pip install -U platformio
 - platformio lib install 561 562
 script:
+- mkdir build
 - platformio ci --build-dir="./build/" --keep-build-dir --lib="." --board=nodemcuv2
 - ls -altr
 - find . -name firmware.elf