Use /bin/sh instead of /bin/bash when possible

[emanuelb]

There are scripts in this repo that are using #!/bin/bash, for some of them it's possible to use #!/bin/sh instead without other modifications:

./trezor/build_pb.sh https://github.com/mycelium-com/wallet-android/blob/1f434c409d9f4dba4e173b6a800bba56dfa63fd8/trezor/build_pb.sh ./mbw/res-sources/updateDrawables.sh https://github.com/mycelium-com/wallet-android/blob/1f434c409d9f4dba4e173b6a800bba56dfa63fd8/mbw/res-sources/updateDrawables.sh ./checkBuild.sh https://github.com/mycelium-com/wallet-android/blob/02bd26f4152999a647fbb40a59da7d51358bc831/checkBuild.sh

Use #!/bin/sh instead of #!/bin/bash when possible, also it might worth to change it for some other scripts if they not relaying to much on bash specific operations (see checkbashisms tool: https://manpages.debian.org/unstable/devscripts/checkbashisms.1.en.html)

[Giszmo]

I guess this is not worth the edit. Many of those scripts are stale anyway and more a reminder how to do things than stuff we use on a daily basis. But thanks for the heads-up.