travis: update the esp-open-sdk version used.

.travis.yml

@@ -2,7 +2,7 @@ language: c
 sudo: false
 env:
   # Target commit for https://github.com/pfalcon/esp-open-sdk/
-  OPENSDK_COMMIT=a48b12f
+  OPENSDK_COMMIT=b069537
   CROSS_ROOT="${HOME}/toolchain-${OPENSDK_COMMIT}"
   CROSS_BINDIR="${CROSS_ROOT}/bin"
   CROSS="ccache xtensa-lx106-elf-"
@@ -32,6 +32,7 @@ addons:
     - python-serial
     - sed
     - git
+    - help2man
     - vim-common
 
 before_install: