build readme typo fix

[Martin Buchholz]

diff --git a/README-builds.html b/README-builds.html
--- a/README-builds.html
+++ b/README-builds.html
@@ -1429,7 +1429,7 @@
                     build output is to go.
                     The default output directory will be build/<i>platform</i>.
                 </dd>
-                <dt><a name="ALT_SLASHJAVA"><tt>ALT_SLASHJAVA</tt></a></dt>
+                <dt><a name="ALT_SLASH_JAVA"><tt>ALT_SLASH_JAVA</tt></a></dt>
                 <dd>
                     The default root location for many of the ALT
path locations
                     of the following ALT variables.