Replace stale tutorial reference links

Tutorial/phase-14-flash-dram/phase-14.md

@@ -50,4 +50,4 @@ DRAM replaces data BRAM at `0x8000_0000-0x8FFF_FFFF`.
 
 - Digilent Arty A7 reference: https://digilent.com/reference/programmable-logic/arty-a7/reference-manual
 - AMD/Xilinx MIG documentation: https://docs.xilinx.com/
-- JEDEC DDR background: https://www.jedec.org/standards-documents/focus/memory-module-design
+- DDR3 SDRAM background: https://en.wikipedia.org/wiki/DDR3_SDRAM