update docs to Java 1.8

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1839863 13f79535-47bb-0310-9956-ffa450edef68

README.rst

 * Official `Apache git mirror`_ at apache.org
 * Unofficial `GitHub git mirror`_ at github.com
 
-Requires Java 1.6 or later.
+Requires Java 1.8 or later.
 
 Contributing
 ------------------
 
-* Download and install svn or git, Java JDK 1.6+, and Apache Ant 1.8+ or Gradle
+* Download and install svn or git, Java JDK 1.8+, and Apache Ant 1.8+ or Gradle
 
 * Check out the code from svn or git
 

build.xml

         <attribute name="src"/>
         <attribute name="dest"/>
         <sequential>
-            <!--fail
-                message="Java version might be uncapable to download https URLs - see https://stackoverflow.com/questions/6851461/java-why-does-ssl-handshake-give-could-not-generate-dh-keypair-exception">
-                <condition>
-                    <and>
-                        <equals arg1="${ant.java.version}" arg2="1.6"/>
-                        <contains string="@{src}" substring="https"/>
-                    </and>
-                </condition>
-            </fail-->
             <get src="@{src}" dest="@{dest}" skipexisting="true"/>
         </sequential>
     </macrodef>