docs: update the default mesa shader cache dir
We renamed the dir in commit 28b326238bcc, this just updates the
website to reflect the change.
diff --git a/docs/envvars.html b/docs/envvars.html
index edc5027..c9733e6 100644
--- a/docs/envvars.html
+++ b/docs/envvars.html
@@ -146,8 +146,8 @@
cache for x86_64 and another 1GB cache for i386.
<li>MESA_GLSL_CACHE_DIR - if set, determines the directory to be used
for the on-disk cache of compiled GLSL programs. If this variable is
-not set, then the cache will be stored in $XDG_CACHE_HOME/mesa (if
-that variable is set), or else within .cache/mesa within the user's
+not set, then the cache will be stored in $XDG_CACHE_HOME/mesa_shader_cache (if
+that variable is set), or else within .cache/mesa_shader_cache within the user's
home directory.
<li>MESA_GLSL - <a href="shading.html#envvars">shading language compiler options</a>
<li>MESA_NO_MINMAX_CACHE - when set, the minmax index cache is globally disabled.