Use ext-intl for heroku.

composer.json

@@ -6,6 +6,7 @@
         "ext-ctype": "*",
         "ext-iconv": "*",
         "ext-mbstring": "*",
+        "ext-intl": "*",
         "doctrine/annotations": "^1.6",
         "friendsofsymfony/ckeditor-bundle": "^2.0",
         "omines/datatables-bundle": "^0.2.2",

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "eaa24e28ac00d9141a07d749b1e94c7d",
+    "content-hash": "f522b3aafd33834efa52b3d0f3c0fd0a",
     "packages": [
         {
             "name": "doctrine/annotations",
@@ -7265,7 +7265,8 @@
         "php": "^7.1.3",
         "ext-ctype": "*",
         "ext-iconv": "*",
-        "ext-mbstring": "*"
+        "ext-mbstring": "*",
+        "ext-intl": "*"
     },
     "platform-dev": []
 }