- composer in php 5.x require increase memory limit

- in PHP 7.3, 7.4 not necessary remove ignore platforms

.travis.yml

@@ -18,17 +18,12 @@ matrix:
     include:
         - php: 5.3
           dist: precise
-          env: COMPOSER_MEMORY_LIMIT=3G
         - php: 5.4
           dist: trusty
         - php: 5.5
           dist: trusty
         - php: 7.0
           env: COVERAGE=1
-        - php: 7.3
-          env: DEPENDENCIES="--ignore-platform-reqs"
-        - php: 7.4
-          env: DEPENDENCIES="--ignore-platform-reqs"
         - php: nightly
           env: DEPENDENCIES="--ignore-platform-reqs"
     exclude:
@@ -58,6 +53,8 @@ before_script:
     - if [ -z "$COVERAGE" ]; then phpenv config-rm xdebug.ini || echo "xdebug not available" ; fi
     ## Composer
     - composer self-update
+    ## Composer in PHP versions 5.x requires 3 GB memory
+    - if [ ${TRAVIS_PHP_VERSION:0:2} == "5." ]; then export COMPOSER_MEMORY_LIMIT=3G ; fi
     - travis_wait composer install --prefer-source $(if [ -n "$DEPENDENCIES" ]; then echo $DEPENDENCIES; fi)
     ## PHPDocumentor
     ##- mkdir -p build/docs