Before errors like this:
```
finder.go:91: error: 'no pom data' for: <Dep ID=com.afollestad.material-dialogs:commons:0.9.6.0 O=false S= >
```
Would be printed to `stderr` but exit code would not be non-zero.
Now the whole `make nix-update-gradle` target should fail if any
dependency resolution fails.
Signed-off-by: Jakub Sokołowski <jakub@status.im>