remove extraneous composer instruction in travis config

Author: michaeldyrynda

.travis.yml

@@ -27,8 +27,6 @@ matrix:
 
 before_install: travis_retry composer require "illuminate/database:${ILLUMINATE_VERSION}" "illuminate/events:${ILLUMINATE_VERSION}" --no-update -v
 
-install: composer update --prefer-source --no-interaction --dev -v
-
 install: travis_retry composer install --prefer-dist --no-interaction --no-suggest -v
 
 script: vendor/bin/phpunit --debug -c phpunit.xml --coverage-clover=coverage.clover