Merge pull request #187 from phil-el/master

Do not fail travis build if the build directory already exists.
diff --git a/.travis.yml b/.travis.yml
index 342a73c..cc88e33 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -24,7 +24,7 @@
   - export VULKAN_SDK=$TRAVIS_BUILD_DIR/$VK_VERSION/x86_64

 

 script:

-  - mkdir build

+  - mkdir -p build

   - cd build

   - cmake ..

   - make