Update db limit of run short description override.

Increase the course run short description override db limit to count
for foreign characters.

LEARNER-4673

course_discovery/apps/course_metadata/migrations/0081_auto_20180329_0718.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.3 on 2018-03-29 07:18
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('course_metadata', '0080_seat_bulk_sku'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='courserun',
+            name='short_description_override',
+            field=models.CharField(blank=True, default=None, help_text="Short description specific for this run of a course. Leave this value blank to default to the parent course's short_description attribute.", max_length=350, null=True),
+        ),
+    ]

course_discovery/apps/course_metadata/models.py

@@ -460,7 +460,7 @@ class CourseRun(TimeStampedModel):
     enrollment_end = models.DateTimeField(null=True, blank=True, db_index=True)
     announcement = models.DateTimeField(null=True, blank=True)
     short_description_override = models.CharField(
-        max_length=255, default=None, null=True, blank=True,
+        max_length=350, default=None, null=True, blank=True,
         help_text=_(
             "Short description specific for this run of a course. Leave this value blank to default to "
             "the parent course's short_description attribute."))