contrib: Update laanwj key

I recently added a signing subkey, which is used to sign gitian
asserts as well as commits.

Old:
```
pub  rsa2048/0x74810B012346C9A6 2011-08-24
uid                             Wladimir J. van der Laan <[email protected]>
sub  rsa2048/0xF69705ED890DE427 2011-08-24
```

New:
```
pub  rsa2048/0x74810B012346C9A6 2011-08-24 [expires: 2019-02-14]
uid                             Wladimir J. van der Laan <[email protected]>
uid                             Wladimir J. van der Laan <[email protected]>
sub  rsa2048/0xF69705ED890DE427 2011-08-24
sub  rsa2048/0x1E4AED62986CD25D 2017-05-17 [expires: 2019-05-17]
sub  rsa2048/0x69B4C4CDC628F8F9 2017-05-17 [expires: 2019-05-17]
```

Author: laanwj