Fix CI error

Author: ruslo

.travis.yml

@@ -57,5 +57,5 @@ install:
 script:
     # download all
     - build.py --toolchain ${TOOLCHAIN} --config ${CONFIG} --verbose --fwd HUNTER_RUN_INSTALL=ON
-    # if run generate again, no download needed
-    - build.py --toolchain ${TOOLCHAIN} --config ${CONFIG} --verbose
+    # if run generate again, no download needed (clear since argument HUNTER_RUN_INSTALL missing)
+    - build.py --toolchain ${TOOLCHAIN} --config ${CONFIG} --verbose --clear