Add reuse tool to CI

.travis.yml

@@ -8,6 +8,9 @@ jdk:
   - openjdk8
   - openjdk11
 
+services:
+  - docker
+
 before_cache:
   - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
   - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
@@ -20,7 +23,11 @@ before_install:
   - export GRADLE_VERSION=6.2
   - wget https://services.gradle.org/distributions/gradle-${GRADLE_VERSION}-all.zip
   - unzip -q gradle-${GRADLE_VERSION}-all.zip
-  - export PATH="$(pwd)/gradle-${GRADLE_VERSION}/bin:$PATH"
+  - rm gradle-${GRADLE_VERSION}-all.zip
+  - sudo mv gradle-${GRADLE_VERSION} /usr/local/bin/
+  - export PATH="/usr/local/bin/gradle-${GRADLE_VERSION}/bin:$PATH"
+  - docker pull fsfe/reuse:latest
+  - docker run -v ${TRAVIS_BUILD_DIR}:/data fsfe/reuse:latest lint
 
 install: gradle assemble --stacktrace