Merge branch 'wip/dueno/bison-bootstrap' into 'master'

Revert "bootstrap.conf: require bison 3.6 or later"

See merge request gnutls/libtasn1!76
diff --git a/bootstrap.conf b/bootstrap.conf
index c8a85b8..45e9689 100644
--- a/bootstrap.conf
+++ b/bootstrap.conf
@@ -42,7 +42,7 @@
 autoconf   2.62
 automake   1.11.1
 git        1.4.4
-bison      3.6
+bison      -
 "
 
 GTKDOCIZE=$(which gtkdocize 2>/dev/null)