fix shell equality operator

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@267669 13f79535-47bb-0310-9956-ffa450edef68

build.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-if [ "$ANT_HOME" == "" ] ; then
+if [ "$ANT_HOME" = "" ] ; then
   ANT_HOME=`pwd`
 fi
 export ANT_HOME