*.sh: Move step backwards. (See full commit message.)

It seems that zsh is giving weird error messages "can't open input file" and
bash doesn't give them. Because of this I must use bash with these scripts.

install.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env zsh
+#!/usr/bin/env bash
 echo "If you are upgrading, press ctrl + c NOW! You have 15 seconds time to cancel this. rerunning this script will overwrite your backups and it makes uninstall.sh useless."
 sleep 15;
 echo "Taking backups..."

uninstall.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env zsh
+#!/usr/bin/env bash
 echo "Restoring default files..."
 cat ~/.zshrc.default.backup > ~/.zshrc
 cat ~/.zsh_aliases.default.backup > ~/.zsh_aliases

upgrade.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env zsh
+#!/usr/bin/env bash
 echo "Backing up files..."
 touch ~/.zshenv
 cat ~/.zshenv > ~/.zshenv.old.backup