[bsp][stm32] add ci for stm32f411-st-nucleo bsp

.travis.yml

@@ -86,6 +86,7 @@ env:
   - RTT_BSP='stm32/stm32f103-fire-arbitrary' RTT_TOOL_CHAIN='sourcery-arm'
   - RTT_BSP='stm32/stm32f407-atk-explorer' RTT_TOOL_CHAIN='sourcery-arm'
   - RTT_BSP='stm32/stm32f407-st-discovery' RTT_TOOL_CHAIN='sourcery-arm'
+  - RTT_BSP='stm32/stm32f411-st-nucleo' RTT_TOOL_CHAIN='sourcery-arm'
   - RTT_BSP='stm32/stm32f429-armfly-v6' RTT_TOOL_CHAIN='sourcery-arm'
   - RTT_BSP='stm32/stm32f429-atk-apollo' RTT_TOOL_CHAIN='sourcery-arm'
   - RTT_BSP='stm32/stm32f429-fire-challenger' RTT_TOOL_CHAIN='sourcery-arm'