Use ESLint to ensure that exports are sorted alphabetically

There's built-in ESLint rule, see `sort-imports`, to ensure that all `import`-statements are sorted alphabetically, since that often helps with readability.
Unfortunately there's no corresponding rule to sort `export`-statements alphabetically, however there's an ESLint plugin which does this; please see https://www.npmjs.com/package/eslint-plugin-sort-exports

The only downside here is that it's not automatically fixable, but the re-ordering is a one-time "cost" and the plugin will help maintain a *consistent* ordering of `export`-statements in the future.
*Note:* To reduce the possibility of introducing any errors here, the re-ordering was done by simply selecting the relevant lines and then using the built-in sort-functionality of my editor.

src/core/function.js

@@ -1345,6 +1345,6 @@ var PostScriptCompiler = (function PostScriptCompilerClosure() {
 export {
   isPDFFunction,
   PDFFunctionFactory,
-  PostScriptEvaluator,
   PostScriptCompiler,
+  PostScriptEvaluator,
 };