shell-scripts: Use [[ instead of [ where possible

Replace all occurrences of [ with [[ in bash and zsh scripts and
configs.
Performance wise it makes sense to use the builtin instead of calling an
external command also when from a functionality stand point `test` would
suffice.

meta/submodules

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-[ $# -eq 1 ] || { echo "Specify what to do" >&2; exit 1; }
+[[ $# -eq 1 ]] || { echo "Specify what to do" >&2; exit 1; }
 
 case "$1" in
 	"--init") INIT=1;;