Fixed typo in Dockerfile (#1985)

Dockerfile

@@ -100,7 +100,7 @@ RUN sed --in-place \
 
 # test overlay build
 ARG RUN_TESTS
-ARG FAIL_ON_TEST_FAILURE=Ture
+ARG FAIL_ON_TEST_FAILURE=True
 RUN if [ -n "$RUN_TESTS" ]; then \
         . $OVERLAY_WS/install/setup.sh && \
         colcon test \