Update shellcheck and shfmt to the latest version.
Fixes <https://github.com/koreader/koreader/issues/5152>.
Btw, you can apply shellcheck suggestions with a command like:
```
shellcheck --include=SC2250 -f diff *.sh | git apply
```
Travis only makes a shallow clone of --depth=50. KOReader is small enough that we can just grab it all. This is necessary to generate the version number, without which some tests will fail.
I'm not entirely sure why something like `git fetch origin master tags/v2015.11` doesn't do the trick, but it doesn't matter much.
