throw error when input to script constructor is not an array

[#58]

test/script.js

@@ -0,0 +1,17 @@
+var Script = require('../src/script.js')
+var assert = require('assert')
+
+describe('Script', function() {
+  describe('constructor', function() {
+    it('works for a byte array', function() {
+      assert.ok(new Script([]))
+    })
+
+    it('throws an error when input is not an array', function() {
+      assert.throws(function(){
+        new Script({})
+      })
+    })
+  })
+
+})