Fix grammar

Signed-off-by: Lukas Reschke <lukas@statuscode.ch>

apps/files/js/files.js

@@ -102,7 +102,7 @@
 			} else if (trimmedName.length === 0) {
 				throw t('files', 'File name cannot be empty.');
 			} else if (OC.fileIsBlacklisted(trimmedName)) {
-				throw t('files', '"{name}" is not an allow filetype', {name: name});
+				throw t('files', '"{name}" is not an allowed filetype', {name: name});
 			}
 
 			return true;