/var/run symlinked to /run in 3.7 image

The `alpine:3.7` image has a symlink from `/var/run` to `/run`, whereas 3.6 and 3.5 did not. Is this intentional? I can't find any notes about it.

The difference threw me off in images like `nginx:1.13.9-alpine`, which just updated from Alpine Linux 3.5 to 3.7 as its base. I run nginx containers as read only and mount a `tmpfs` volume at `/var/run`. This broke with the symlink.

`alpine:3.7`
```
/ # ls -al /var
total 44
drwxr-xr-x 11 root root 4096 Jan 9 19:37 .
drwxr-xr-x 1 root root 4096 Mar 15 23:23 ..
drwxr-xr-x 4 root root 4096 Jan 9 19:37 cache
dr-xr-xr-x 2 root root 4096 Jan 9 19:37 empty
drwxr-xr-x 5 root root 4096 Jan 9 19:37 lib
drwxr-xr-x 2 root root 4096 Jan 9 19:37 local
drwxr-xr-x 3 root root 4096 Jan 9 19:37 lock
drwxr-xr-x 2 root root 4096 Jan 9 19:37 log
drwxr-xr-x 2 root root 4096 Jan 9 19:37 opt
lrwxrwxrwx 1 root root 4 Jan 9 19:37 run -> /run
drwxr-xr-x 3 root root 4096 Jan 9 19:37 spool
drwxrwxrwt 2 root root 4096 Jan 9 19:37 tmp
```

`alpine:3.6`
```
/var # ls -al /var
total 48
drwxr-xr-x 12 root root 4096 Jan 9 19:36 .
drwxr-xr-x 1 root root 4096 Mar 15 23:18 ..
drwxr-xr-x 4 root root 4096 Jan 9 19:36 cache
dr-xr-xr-x 2 root root 4096 Jan 9 19:36 empty
drwxr-xr-x 5 root root 4096 Jan 9 19:36 lib
drwxr-xr-x 2 root root 4096 Jan 9 19:36 local
drwxr-xr-x 3 root root 4096 Jan 9 19:36 lock
drwxr-xr-x 2 root root 4096 Jan 9 19:36 log
drwxr-xr-x 2 root root 4096 Jan 9 19:36 opt
drwxr-xr-x 2 root root 4096 Jan 9 19:36 run
drwxr-xr-x 3 root root 4096 Jan 9 19:36 spool
drwxrwxrwt 2 root root 4096 Jan 9 19:36 tmp
```