Build: Update GCC default version to 10.3

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I5a958ab2b25ad1eb933e833a41c67fbdee552b22
diff --git a/build-docs.sh b/build-docs.sh
index 569eb2d..bbf4580 100755
--- a/build-docs.sh
+++ b/build-docs.sh
@@ -13,7 +13,7 @@
 
 set -ex
 
-export PATH=$PATH:$GCC_7_3_1_PATH
+export PATH=$PATH:$GCC_10_3_PATH
 
 mkdir -p ${WORKSPACE}/trusted-firmware-m/build/docs
 cd ${WORKSPACE}/trusted-firmware-m/build/docs