[GH-3777] Keep using dependencies that were stable during 2.10 branch off.

.appveyor.yml

@@ -117,7 +117,6 @@ install:
         }
     # install composer dependencies
     - cd C:\projects\dbal
-    - rm composer.lock
     - appveyor-retry composer self-update
     - appveyor-retry composer install --no-progress --prefer-dist
 

.travis.yml

@@ -18,8 +18,7 @@ before_script:
   - if [[ "$DB" == "mysql" || "$DB" == "mysqli" || "$DB" == *"mariadb"* ]]; then mysql < tests/travis/create-mysql-schema.sql; fi;
 
 install:
-  - rm composer.lock
-  - travis_retry composer -n update --prefer-dist
+  - travis_retry composer -n install --prefer-dist
 
 script:
   - |