Merge pull request #5672 from owncloud/fixing-5668-master-2

fixing Specified key was too long; max key length is 767 bytes

db_structure.xml

@@ -884,7 +884,7 @@
 				<type>text</type>
 				<default></default>
 				<notnull>true</notnull>
-				<length>256</length>
+				<length>255</length>
 			</field>
 
 			<field>