gnu: ams-lv2: Fix error in configure phase.

Python 3.7 introduced PEP 479. That raised an error in an old waf-script
included in the package. An updated waf-script was found in a
newer commit that fixes the problem.

* gnu/packages/music.scm (ams-lv2)[sources]: Update, using two more commits
than version 1.2.1.

gnu/packages/music.scm

@@ -18,6 +18,7 @@
 ;;; Copyright © 2018 Stefan Reichör <stefan@xsteve.at>
 ;;; Copyright © 2018 Pierre Neidhardt <mail@ambrevar.xyz>
 ;;; Copyright © 2018 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018 Björn Höfling <bjoern.hoefling@bjoernhoefling.de>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -2285,19 +2286,24 @@ follows a traditional multi-track tape recorder control paradigm.")
     (license license:gpl2+)))
 
 (define-public ams-lv2
+  ;; Version 1.2.1 built with Python 3.7 raises an error in the waf-script.
+  ;; Therefore, we take two more commmits than 1.2.1 that introduce an updated
+  ;; waf-script and fix one error.
+  (let ((commit "377d166db54a787b48979171c5652d2eb4f1bbb5")
+        (revision "1"))
     (package
       (name "ams-lv2")
-    (version "1.2.1")
+      (version (git-version "1.2.1" revision commit))
       (source
        (origin
          (method git-fetch)
          (uri (git-reference
                (url "https://github.com/blablack/ams-lv2.git")
-             (commit version)))
+               (commit commit)))
          (file-name (git-file-name name version))
          (sha256
           (base32
-         "1n1dnqnj24xhiy9323lj52nswr5120cj56fpckg802miss05sr6x"))))
+           "1ndgxcxjxwidg7436k0nb5clxkyi878k1j999sbbd1gk2fm0kcqm"))))
       (build-system waf-build-system)
       (arguments
        `(#:phases
@@ -2325,7 +2331,7 @@ follows a traditional multi-track tape recorder control paradigm.")
 found in Alsa Modular Synth.  These plugins are used to create modular
 synthesizers and contain: VCO, VCF, VCA, LFO, slew limiter, envelopes, sample
 and hold, etc.")
-    (license license:gpl2)))
+      (license license:gpl2))))
 
 (define-public gxtuner
   (package