Update MongoDB extension on travis to make the builds green again.

.travis.yml

@@ -100,8 +100,6 @@ before_install:
       [[ $PHP = 5.* ]] && echo extension = memcache.so >> $INI
       if [[ $PHP = 5.* ]]; then
           echo extension = mongo.so >> $INI
-      elif [[ $PHP = 7.* ]]; then
-          echo extension = mongodb.so >> $INI
       fi
 
       # Matrix lines for intermediate PHP versions are skipped for pull requests
@@ -127,6 +125,7 @@ before_install:
           tfold ext.apcu4 'echo yes | pecl install -f apcu-4.0.11'
       elif [[ ! $skip && $PHP = 7.* ]]; then
           tfold ext.apcu5 'echo yes | pecl install -f apcu-5.1.6'
+          tfold ext.mongodb pecl install -f mongodb-1.4.0RC1
       fi
 
 install: