fix(ci): Use meson from backports

.gitlab-ci.yml

@@ -3,7 +3,10 @@ image: "debian"
 build:
     stage: build
     before_script:
-        - apt update -qq && apt install -y -qq gcc-arm-none-eabi python3-pip meson
+        - echo "deb http://deb.debian.org/debian stretch-backports main" >> /etc/apt/sources.list
+        - apt update -qq
+        - apt install -y -qq gcc-arm-none-eabi python3-pip
+        - apt install -y -qq -t stretch-backports install meson
         - pip3 install crc16
     script:
         - cd bootloader