fix: add newline at the end of file

Most editors are configured to add a newline at the end of the file while Babel strips the last line when transforming. This means that if we manually edit the output fixtures, there's always a mismatch in the code due to the extra new line. We workaround this by always adding a new line at the end of the file

src/__fixtures__/function-expression/output.js

@@ -1 +1 @@
-const oof = rab => rab;
+const oof = rab => rab;

src/__fixtures__/simple-variable/output.js

@@ -1 +1 @@
-var eltit = 'hello world';
+var eltit = 'hello world';

src/index.js

@@ -118,7 +118,7 @@ exports.create = function create(config) {
     }).then(
       ({ code }) => ({
         filename: output,
-        content: code,
+        content: code + '\n',
         stack,
       }),
       e => ({
@@ -127,10 +127,11 @@ exports.create = function create(config) {
         // Strip them so the error is more readable
         // Also replace the current working directory with a placeholder
         // This makes sure that the stacktraces are same across machines
-        content: stripAnsi(e.stack).replace(
-          new RegExp(escapeRegexp(process.cwd()), 'g'),
-          '<cwd>'
-        ),
+        content:
+          stripAnsi(e.stack).replace(
+            new RegExp(escapeRegexp(process.cwd()), 'g'),
+            '<cwd>'
+          ) + '\n',
         stack,
       })
     );