fix ubuntu 12.04 compilation error on clientCheck.ml

```
Linking CXX static library libhphp_analysis.a
[ 39%] Built target hphp_analysis
File "clientCheck.ml", line 266, characters 30-314:
Error: This expression has type string but an expression was expected of type
         ('a, out_channel, unit) format =
           ('a, out_channel, unit, unit, unit, unit) format6
make[5]: *** [clientCheck.cmx] Error 2
make[4]: *** [rec.opt] Error 1
make[3]: *** [opt] Error 2
make[2]: *** [hphp/hack/CMakeFiles/hack] Error 2
make[1]: *** [hphp/hack/CMakeFiles/hack.dir/all] Error 2
make: *** [all] Error 2
```