MINOR: acl: Add HTTP_2.0 predefined macro

HTTP_2.0 predefined macro returns true for HTTP/2 requests. HTTP/2 doen't
convey a version information, so this macro may seem a bit strange. But for
compatiblity reasons, internally, the "HTTP/2.0" version is set. Thus, it is
handy to rely on it to differenciate HTTP/1 and HTTP/2 requests.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index c25e2ce..6b52609 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -19503,6 +19503,7 @@
 HTTP             req.proto_http                     match if request protocol is valid HTTP
 HTTP_1.0         req.ver 1.0                        match if HTTP request version is 1.0
 HTTP_1.1         req.ver 1.1                        match if HTTP request version is 1.1
+HTTP_2.0         req.ver 2.0                        match if HTTP request version is 2.0
 HTTP_CONTENT     req.hdr_val(content-length) gt 0   match an existing content-length in the HTTP request
 HTTP_URL_ABS     url_reg ^[^/:]*://                 match absolute URL with scheme
 HTTP_URL_SLASH   url_beg /                          match URL beginning with "/"
diff --git a/src/acl.c b/src/acl.c
index 54324c5..655f9f4 100644
--- a/src/acl.c
+++ b/src/acl.c
@@ -755,6 +755,7 @@
 	{ .name = "HTTP",           .expr = {"req.proto_http",""}},
 	{ .name = "HTTP_1.0",       .expr = {"req.ver","1.0",""}},
 	{ .name = "HTTP_1.1",       .expr = {"req.ver","1.1",""}},
+	{ .name = "HTTP_2.0",       .expr = {"req.ver","2.0",""}},
 	{ .name = "METH_CONNECT",   .expr = {"method","CONNECT",""}},
 	{ .name = "METH_DELETE",    .expr = {"method","DELETE",""}},
 	{ .name = "METH_GET",       .expr = {"method","GET","HEAD",""}},