add error for sourcePath

Author: barak007

lib/map-generator.js

@@ -202,7 +202,11 @@ class MapGenerator {
     if (this.mapOpts.from) {
       return this.toUrl(this.mapOpts.from)
     } else if (this.mapOpts.absolute) {
-      return pathToFileURL(node.source.input.from).toString()
+      if(pathToFileURL) {
+        return pathToFileURL(node.source.input.from).toString()
+      } else {
+        throw new Error('map option "absolute" is not available in this postcss build')
+      }
     } else {
       return this.toUrl(this.path(node.source.input.from))
     }