README.md: Update Vivado's version number

README.md

@@ -3,7 +3,7 @@
 Analog Devices HDL libraries and projects
 
 ###Tools version:
-- **Xilinx** : [Vivado 2014.4.1]
+- **Xilinx** : [Vivado 2015.2.1]
 - **Altera** : [Quartus 15.0]
 
 ###Documentation and support
@@ -12,7 +12,7 @@ For first time users, it is **highly recommended** to go through our [HDL user g
 
 For support please visit our [FPGA Reference Designs Support Community] on EngineerZone.
 
-[Vivado 2014.4.1]:http://www.xilinx.com/content/xilinx/en/downloadNav/vivado-design-tools/2014-4.html
+[Vivado 2015.2.1]:http://www.xilinx.com/content/xilinx/en/downloadNav/vivado-design-tools/2015-2.html
 [Quartus 15.0]:http://dl.altera.com/15.0/?edition=subscription
 [HDL user guide]:http://wiki.analog.com/resources/fpga/docs/hdl
 [FPGA Reference Designs Support Community]:http://ez.analog.com/community/fpga