add nrf52840 self-test, use addon pip3 to install adafruit-nrfutil (espressif#42)

* add nrf52840 self-test, use addon pip3 to install adafruit-nrfutil

* add setuptools to be safe

Author: hathach

.travis.yml

@@ -7,7 +7,16 @@ cache:
 git:
   depth: false
   quiet: true
+
+addons:
+  apt:
+    packages:
+      - python3
+      - python3-pip
+      - python3-setuptools
+
 before_install:
+  - pip3 install --user adafruit-nrfutil
   - source $TRAVIS_BUILD_DIR/install.sh
 script:
   - build_platform esp32
@@ -16,6 +25,7 @@ script:
   - build_platform zero
   - build_platform esp8266
   - build_platform m4
+  - build_platform nrf52840
 
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