composer/bin/coveralls chmod +x made

composer status always shows composer/bin/coveralls as changed file:

composer status -v
You have changes in the following dependencies:
```
...
    M composer/bin/coveralls
```

git diff

```
diff --git a/composer/bin/coveralls b/composer/bin/coveralls
old mode 100644
new mode 100755
```

So, my pull request should help with that.
Please merge it, thank you.