Merge remote-tracking branch 'origin/MAGETWO-39005-mbstring-dependency' into PR_Branch

Conflicts:
	composer.lock

Author: Olga Kopylova

composer.json

@@ -55,6 +55,7 @@
         "ext-iconv": "*",
         "ext-intl": "*",
         "ext-xsl": "*",
+        "ext-mbstring": "*",
         "sjparkinson/static-review": "~4.1",
         "fabpot/php-cs-fixer": "~1.2",
         "lusitanian/oauth": "~0.3"