set locale in mbed-os-env docker image

Author: saheerb

docker_images/mbed-os-env/Dockerfile

@@ -2,6 +2,11 @@
 # Pull base image
 FROM ubuntu:20.04
 
+# ------------------------------------------------------------------------------
+# set locale
+ENV LANG C.UTF-8
+ENV LC_ALL C.UTF-8
+
 # ------------------------------------------------------------------------------
 # Arguments
 ARG WORKDIR=/root