ci: explicitly specify tools versions

This makes our builds more stable and also allows us to track what versions do we use and update
them as other dependencies.

Author: php-coder

.travis.yml

@@ -20,10 +20,10 @@ before_script:
       mysql -u root -e 'CREATE DATABASE mystamps CHARACTER SET utf8;';
       mkdir -p /tmp/uploads /tmp/preview;
       cp src/main/resources/test/test.png /tmp/uploads/1.png;
-      npm install -g bootlint;
-      pip install --user html5validator==0.3.3 robotframework-lint==1.1 ansible==2.9.2 ansible-lint;
+      npm install -g bootlint@1.1.0;
+      pip install --user html5validator==0.3.3 robotframework-lint==1.1 ansible==2.9.2 ansible-lint==4.2.0;
       if [ "$TRAVIS_PULL_REQUEST" != 'false' ]; then
-        gem install danger nokogiri --no-document;
+        gem install danger:8.2.2 nokogiri:1.10.10 --no-document;
       fi;
       sudo apt-get -qq update;
       sudo apt-get install -y shellcheck;