(fix): don't mutate process.argv with arr.splice

- 1.7.1 introduced some arr.splice's into the code, which caused
  mutations in process.argv, affecting downstream code

- set arr to a clone of process.argv instead so it can be freely
  mutated after
- explicitly call the parameter processArgv so code is written more
  carefully when dealing with it
- add a test to ensure process.argv is not mutated

lib/index.js

@@ -105,7 +105,8 @@ class Sade {
 		return this;
 	}
 
-	parse(arr, opts={}) {
+	parse(processArgv, opts={}) {
+		let arr = processArgv.slice(); // DON'T mutate process.argv, clone first
 		let offset=2, tmp, idx, isVoid, cmd;
 		let alias = { h:'help', v:'version' };
 		let argv = mri(arr.slice(offset), { alias });

test/index.js

@@ -212,6 +212,20 @@ test('prog.action (multi optional)', t => {
 	(c=true) && run(); // +4 tests
 });
 
+test('prog.parse', t => {
+	t.plan(1);
+
+	let ctx = sade('foo')
+		.command('build')
+		.action(() => {});
+
+	let args = ['', '', 'build'];
+	let argsCopy = args.slice();
+	ctx.parse(argsCopy);
+
+	t.deepEqual(argsCopy, args, '~> process.argv is not mutated');
+});
+
 test('prog.parse :: lazy', t => {
 	t.plan(14);