Update travis.yml for CMake build with IDF v3.3.

.travis.yml

@@ -29,15 +29,13 @@ install:
   # Make xtensa-esp32-elf available for all terminal sessions
   - export PATH=$PATH:$HOME/esp/xtensa-esp32-elf/bin
   # Get ESP-IDF from github
-  - git clone --recursive --branch release/v3.0 https://github.com/espressif/esp-idf.git
+  - git clone --recursive --branch release/v3.3 https://github.com/espressif/esp-idf.git
   # Set the path to ESP-IDF directory
   - export IDF_PATH=~/esp/esp-idf
+  # Install python dependencies
+  - pip install --user -r $IDF_PATH/requirements.txt
 
 script:
-  # Go back to the git repository
+  # Build project within the original repository
   - cd $PROJECT_PATH
-  # Update configuration so that kconfig doesn't start interactive mode
-  - make defconfig
-  # Build project from the git repository
-  - make
-
+  - $IDF_PATH/tools/idf.py build