Pass basedir to Babel (#264)

* Upgrade Babel to beta.46 & upgrade tap to fix SIGPROF warnings.

* Pass basedir to Babel for correct relative paths in source maps.

* Fix error test regex.

* Upgrade to Babel beta.47

* ci: Drop Node 4; add Node 10

.travis.yml

@@ -1,9 +1,6 @@
 sudo: false
 language: node_js
 node_js:
+  - "10"
   - "8"
   - "6"
-  - "4"
-
-before_install:
-  - npm install -g npm@5

index.js

@@ -62,7 +62,7 @@ Babelify.configure = function (opts) {
   if (opts.plugins && opts.plugins._) opts.plugins = opts.plugins._;
   if (opts.presets && opts.presets._) opts.presets = opts.presets._;
 
-  return function (filename) {
+  return function (filename, topts) {
     var extname = path.extname(filename);
     if (extensions.indexOf(extname) === -1) {
       return stream.PassThrough();
@@ -72,6 +72,8 @@ Babelify.configure = function (opts) {
       ? Object.assign({sourceFileName: filename}, opts)
       : opts;
 
+    if (topts && topts._flags && topts._flags.basedir) _opts.cwd = topts._flags.basedir;
+
     return new Babelify(filename, _opts);
   };
 };