use a trailing return type for this function

2 adjacent parameters of 'setFolderPermissions' of similar type are easily swapped by mistake

File src/common/filesystembase.cpp does not conform to Custom style guidelines. (lines 152, 153, 154, 155, 156, 158, 159, 160, 195, 196)

File src/libsync/filesystem.cpp does not conform to Custom style guidelines. (lines 31, 199, 206, 221, 246, 316)

File src/libsync/filesystem.h does not conform to Custom style guidelines. (lines 19, 100, 101)

File src/libsync/owncloudpropagator.cpp does not conform to Custom style guidelines. (lines 1457, 1458, 1459, 1460, 1465, 1466, 1467, 1471, 1472, 1473, 1475, 1476, 1482, 1483, 1484, 1485, 1490, 1491, 1492, 1496, 1497, 1498, 1500, 1501, 1521)

File src/libsync/propagatedownload.cpp does not conform to Custom style guidelines. (lines 687, 688, 1298, 1299)

File src/libsync/propagatorjobs.cpp does not conform to Custom style guidelines. (lines 35, 200, 201, 213, 214, 215, 216, 220, 221, 234, 235, 320, 321, 338, 339, 344, 350, 351, 353)

File test/testpermissions.cpp does not conform to Custom style guidelines. (lines 119, 122, 124, 128, 132, 135, 136, 138, 141, 145, 148, 152, 154, 160, 239, 319, 322, 598, 709, 712, 726, 729)