Fix shebang preservation (#417)

src/index.js

@@ -353,7 +353,7 @@ async function getEntries({ input, cwd }) {
 	return entries;
 }
 
-// shebang cache map thing because the transform only gets run once
+// shebang cache map because the transform only gets run once
 const shebang = {};
 
 function createConfig(options, entry, format, writeMeta) {
@@ -507,24 +507,13 @@ function createConfig(options, entry, format, writeMeta) {
 					}),
 					json(),
 					{
-						// Custom plugin that removes shebang from code because newer
-						// versions of bublé bundle their own private version of `acorn`
-						// and I don't know a way to patch in the option `allowHashBang`
-						// to acorn.
-						// See: https://github.com/Rich-Harris/buble/pull/165
-						transform(code) {
-							let reg = /^#!(.*)/;
-							let match = code.match(reg);
-
-							shebang[options.name] = match ? '#!' + match[1] : '';
-
-							code = code.replace(reg, '');
-
-							return {
-								code,
-								map: null,
-							};
-						},
+						// We have to remove shebang so it doesn't end up in the middle of the code somewhere
+						transform: code => ({
+							code: code.replace(/^#![^\n]*/, bang => {
+								shebang[options.name] = bang;
+							}),
+							map: null,
+						}),
 					},
 					useTypescript &&
 						typescript({