gnu: bedtools-2.18: Fetch sources from stable URL.

* gnu/packages/bioinformatics.scm (bedtools-2.18)[source]: Use stable release
tarball instead of generated tag tarball.

gnu/packages/bioinformatics.scm

@@ -438,11 +438,11 @@ BED, GFF/GTF, VCF.")
     (source (origin
               (method url-fetch)
               (uri (string-append "https://github.com/arq5x/bedtools2/"
-                                  "archive/v" version ".tar.gz"))
+                                  "releases/download/v" version
-              (file-name (string-append name "-" version ".tar.gz"))
+                                  "/bedtools-" version ".tar.gz"))
               (sha256
                (base32
-                "05vrnr8yp7swfagshzpgqmzk1blnwnq8pq5pckzi1m26w98d63vf"))))
+                "11rvca19ncg03kxd0wzlfx5ws7r3nisd0z8s9j9n182d8ksp2pxz"))))
     (arguments
      '(#:test-target "test"
        #:phases