fix problems with TravisCi

Added composer.lock to ignored files, Travis
could not install php_cs because it was
missing in lock file.
Removed require for mysqli extension, Travis will
fail because it hasn't this extension installed.

Author: Filip Marek

.gitignore

@@ -2,4 +2,7 @@
 .idea
 
 # ignore Composer downloads
-/vendor/*
+/vendor/*
+
+# ignore Composer.lock
+composer.lock

composer.json

@@ -12,8 +12,7 @@
     ],
     "require": {
         "php": ">=5.6.0",
-        "squizlabs/php_codesniffer": "^3.0@dev",
-        "ext-mysqli": "*"
+        "squizlabs/php_codesniffer": "^3.0@dev"
     },
     "autoload": {
         "psr-4": {