Fix build on OS X 10.7
http://icculus.org/pipermail/physfs/2018-March/001255.html
--- src/physfs_platform_apple.m.old	2018-03-20 11:30:49.000000000 -0600
+++ src/physfs_platform_apple.m	2018-03-20 11:31:12.000000000 -0600
@@ -50,7 +50,7 @@
     {
         NSArray *paths = NSSearchPathForDirectoriesInDomains(NSApplicationSupportDirectory, NSUserDomainMask, TRUE);
         BAIL_IF(!paths, PHYSFS_ERR_OS_ERROR, NULL);
-        NSString *path = (NSString *) paths[0];
+        NSString *path = (NSString *) [paths objectAtIndex:0];
         BAIL_IF(!path, PHYSFS_ERR_OS_ERROR, NULL);
         size_t len = [path lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
         const size_t applen = strlen(app);