one more improvement of Travis CI 'Raspberry PI' target

.travis.yml

@@ -1,4 +1,5 @@
 language: c
+dist: bionic
 env:
   global:
     - ARDUINO_IDE_VERSION=1.8.5
@@ -24,7 +25,7 @@ before_install:
       rm energia-$ENERGIA_IDE_VERSION-linux64.tar.xz ;
       sudo mv energia-$ENERGIA_IDE_VERSION /usr/local/share/energia ;
       sudo ln -s /usr/local/share/energia/energia /usr/local/bin/energia ;
-    else if [[ "$BOARD" =~ "raspberry:" ]]; then
+    else if [[ "$BOARD" =~ "raspberry" ]]; then
         sleep 1 ;
       else
         wget http://downloads.arduino.cc/arduino-$ARDUINO_IDE_VERSION-linux64.tar.xz ;
@@ -38,7 +39,7 @@ install:
   - if [[ "$BOARD" =~ "energia:" ]]; then
       mkdir $HOME/Energia ;
       ln -s $PWD/software/firmware/source/libraries $HOME/Energia/libraries ;
-    else if [[ "$BOARD" =~ "raspberry:" ]]; then
+    else if [[ "$BOARD" =~ "raspberry" ]]; then
         sudo ln -s /usr/bin/aclocal /usr/local/bin/aclocal-1.16 ;
         sudo ln -s /usr/bin/automake /usr/local/bin/automake-1.16 ;
       else