[gnome-latex] readme: emphasize Vala = 0.40, not >= 0.40

[Sébastien Wilmet <swilmet src gnome org>]

commit 40b0b69cce7d9c81c43e599d50ca134ea35f1c48
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Wed Oct 24 17:38:51 2018 +0200

    readme: emphasize Vala = 0.40, not >= 0.40
    
    For the reason, see:
    - commit f24c864519e6e7108a4b56574278c67b79f6679d
    - https://gitlab.gnome.org/GNOME/gnome-latex/issues/59
    - and other related issues and commits between 3.28 and 3.30.
    
    At least one crash has been properly fixed, another set of crashes has
    been worked around, but more crashes have been discovered.
    
    When creating a package for gnome-latex, it's better to take the
    tarball, without re-running valac (so by keeping the generated C code).

 README | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README b/README
index 0b68263..d2ff3c6 100644
--- a/README
+++ b/README
@@ -30,7 +30,7 @@ Dependencies
 * Latexmk >= 4.31 (optional, but strongly recommended)
 
 And for building the sources:
-* Vala 0.40 (may be optional)
+* Vala = 0.40 (may be optional), attention GNOME LaTeX cannot be built with Vala >= 0.42.
 * yelp-tools
 
 If you are installing GNOME LaTeX from a tarball, you don't have to install