Issue #201: Update travis to check against PHP7.4

Travis, PGSQL 9.5.
Default distro.
PHP 7.4 check added on M39/master.

.travis.yml

@@ -2,15 +2,16 @@ language: php
 
 sudo: true
 
+services:
+  - mysql
+
 addons:
   firefox: "47.0.1"
-  postgresql: "9.4"
+  postgresql: "9.5"
   apt:
     packages:
     - openjdk-8-jre
 
-dist: trusty
-
 cache:
   directories:
   - $HOME/.composer/cache
@@ -26,8 +27,6 @@ env:
   - DB=pgsql  MOODLE_BRANCH=MOODLE_38_STABLE
   - DB=pgsql  MOODLE_BRANCH=MOODLE_39_STABLE
   - DB=mysqli MOODLE_BRANCH=MOODLE_39_STABLE
-  - DB=pgsql  MOODLE_BRANCH=master
-  - DB=mysqli MOODLE_BRANCH=master
 
 matrix:
   include:
@@ -37,13 +36,13 @@ matrix:
       env: DB=mysqli MOODLE_BRANCH=MOODLE_35_STABLE
     - php: 7.1
       env: DB=mysqli MOODLE_BRANCH=MOODLE_33_STABLE NODEJS=8
+    - php: 7.4
+      env: DB=mysqli MOODLE_BRANCH=master
+    - php: 7.4
+      env: DB=pgsql MOODLE_BRANCH=master
 
 before_install:
   - export MOODLE_VERSION=$(echo "$MOODLE_BRANCH" | cut -d'_' -f 2)
-  - if [ ${TRAVIS_PHP_VERSION:0:3} == "7.2" ] && [ $DB == "pgsql" ] && [[ "$MOODLE_VERSION" -gt 38 || "$MOODLE_VERSION" == "master" ]] ; then
-      sudo /etc/init.d/postgresql stop;
-      sudo /etc/init.d/postgresql start 9.5;
-    fi
   - phpenv config-rm xdebug.ini
   - if [ "$NODEJS" = 8 ]; then
       nvm install 8.9;