Update python-pep to 2.1.0-rc1.

This is the first version actually using libpEpAdapter.

pEp/nightly.scm

@@ -208,16 +208,16 @@ adapters.")
 (define-public python-pep
   (package
     (name "python-pep")
-    (version "2.1.0-rc0")
+    (version "2.1.0-rc1")
     (source
      (origin
        (method hg-fetch)
        (uri (hg-reference
              (url "https://pep.foundation/dev/repos/pEpPythonAdapter")
-             (changeset "671d9e268e71"))) ;; r376
+             (changeset "2526edfff797"))) ;; r392
        (file-name (string-append name "-" version "-checkout"))
        (sha256
-        (base32 "01r52nzr5dln6jbrnvdah9z5ksh91y9gbxfhddvzxxrv5dr8v15y"))))
+        (base32 "1ychv58im1b94kd63q796bq0nilcrr4czmbxab1smwxsshf2im7w"))))
     (build-system python-build-system)
     (arguments
      `(;; Adding configure-flags does not work, running `build_ext`
@@ -244,7 +244,9 @@ adapters.")
                (("^(\\s+SYS_LIB_PREFIXES = )\\['/usr.*" _ a)
                 (string-append a "os.getenv('LIBRARY_PATH', '').split(os.pathsep)\n"))
                (("^(\\s+SYS_SHARES = )\\['/usr.*" _ a)
-                (string-append a "['" (assoc-ref %build-inputs "asn1c") "/share']\n")))
+                (string-append a "['" (assoc-ref %build-inputs "asn1c") "/share']\n"))
+               (("^(\\s+package_dir=).*" _ a)
+                (string-append a "{'': 'src'}, packages=['pEp'],\n")))
              #t)))))
     (inputs
      `(("pep-engine" ,pep-engine)