apkbuild-lint: allow double underscore as argument
apkbuild-lint guards against parameters starting with a double underscore as they are reserved. But the check for this is a bit too eager and also warns when something starts with a double underscore which is not a variable.
For example:
function foo() {
make -D__VAR=value
}
is a legal construct, but this resulted in a warning. This is because the start-of-string / tab part was marked optional, which makes the test look for anything starting with a double underscore.
Remove the ?
from the group to actual anchor the check.
Fixes #24 (closed)