README update STM32L5 to CUBE V1.4.0

Author: JeanMarcR

targets/TARGET_STM/README.md

@@ -73,7 +73,7 @@ This table summarizes the STM32Cube versions currently used in Mbed OS master br
 | L0          |    1.12.0    | https://github.com/STMicroelectronics/STM32CubeL0 |
 | L1          |    1.10.2    | https://github.com/STMicroelectronics/STM32CubeL1 |
 | L4          |    1.17.0    | https://github.com/STMicroelectronics/STM32CubeL4 |
-| L5          |    1.3.0     | https://github.com/STMicroelectronics/STM32CubeL5 |
+| L5          |    1.4.0     | https://github.com/STMicroelectronics/STM32CubeL5 |
 | WB          |    1.11.1    | https://github.com/STMicroelectronics/STM32CubeWB |
 | WL          |    1.0.0     | https://github.com/STMicroelectronics/STM32CubeWL |