Fix Bashisms

The default /bin/sh in some places isn't bash (like Ubuntu, dash) and
the script is using Bashisms:

```
[1005][rubiojr@octox] checkbashisms -f script/test
possible bashism in script/test line 7 (alternative test command ([[ foo
]] should be [ foo ])):
if [[ "$#" != "0" ]]; then
```

So trying to run it results in:

```
./script/test: 7: ./script/test: [[: not found
^Cexit status 2
```

script/test

@@ -4,7 +4,7 @@
 
 target="./..."
 
-if [[ "$#" != "0" ]]; then
+if [ "$#" != "0" ]; then
   target="./$@"
 fi