README: fix stlink instructions

Since 31c58c139d there is a unified config
for all stlink versions.

Change-Id: Id736063496ecd96e2024ed69dcb67a22c44b80bb
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/4672
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

README

@@ -42,7 +42,7 @@ e.g.:
   openocd -f interface/ftdi/jtagkey2.cfg -c "transport select jtag" \
           -f target/ti_calypso.cfg
 
-  openocd -f interface/stlink-v2-1.cfg -c "transport select hla_swd" \
+  openocd -f interface/stlink.cfg -c "transport select hla_swd" \
           -f target/stm32l0.cfg
 
 After OpenOCD startup, connect GDB with