configure: Use camel case for UNIX sockets feature output

To match the curl --version output.
diff --git a/configure.ac b/configure.ac
index 2cfef5a..100d9c5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3391,7 +3391,7 @@
   SUPPORT_FEATURES="$SUPPORT_FEATURES IPv6"
 fi
 if test "x$USE_UNIX_SOCKETS" = "x1"; then
-  SUPPORT_FEATURES="$SUPPORT_FEATURES unix-sockets"
+  SUPPORT_FEATURES="$SUPPORT_FEATURES UNIX-Sockets"
 fi
 if test "x$HAVE_LIBZ" = "x1"; then
   SUPPORT_FEATURES="$SUPPORT_FEATURES libz"