Installing ninja on travis build.
diff --git a/.travis.yml b/.travis.yml
index 19af796..28667cb 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,6 +16,7 @@
 
 before_script:
     - pip3 install --upgrade pip
+    - pip3 install --user ninja
     - pip3 install --user meson
 
 script: