Fix "mutagen" dependency.

For whatever reason base package name for "mutagen" refers to the
Python 2 version, with a "python-mutagen" for Python 3.

.SRCINFO

@@ -7,7 +7,7 @@ pkgbase = beets-python3-git
 	license = MIT
 	makedepends = git
 	depends = python-munkres
-	depends = mutagen
+	depends = python-mutagen
 	depends = python-setuptools
 	depends = python-unidecode
 	depends = python-musicbrainzngs

PKGBUILD

@@ -8,7 +8,7 @@ pkgdesc="Flexible music library manager and tagger - git version"
 arch=('any')
 url="http://beets.io/"
 license=('MIT')
-depends=('python-munkres' 'mutagen'
+depends=('python-munkres' 'python-mutagen'
          'python-setuptools' 'python-unidecode'
          'python-musicbrainzngs' 'python-yaml'
          'python-jellyfish' 'python-six')