Fix a bug in assert_ndk_version.sh

The version parsing code was hard coding the fact that the
desired version is of the form

r + NUMERIC_MAJOR_VERSION + ALPHABETIC_MINOR_VERSION

r10 release of the NDK does not have a minor version an it breaks
the logic.

The fix is to make the version extraction be more robust to the
optional presence of the minor version.

Change-Id: Iace13ae7cad8cbd93ed635ecf7f1dce3a3ae15d5

jni/assert_ndk_version.sh

diff --git a/jni/assert_ndk_version.sh b/jni/assert_ndk_version.sh
index 7a56c23..0704492 100755
--- a/jni/assert_ndk_version.sh
+++ b/jni/assert_ndk_version.sh
@@ -45,7 +45,7 @@
 # 'r9d (64-bit)' and versions >= 10.
 function get_major_minor() {
   # r9d (64-bit) -> '9d', also handle versions >= 10.
-  local version=$(echo "$1" | sed 's/r\([0-9]\{1,2\}[a-z]\).*/\1/')
+  local version=$(echo "$1" | sed 's/r\([0-9]\{1,2\}[a-z]\{0,1\}\).*/\1/')
   local major=$(echo "$version" | sed 's/\([0-9]\{1,2\}\).*/\1/')
   local minor=$(echo "$version" | sed 's/^[0-9]*//')
   echo "$major $minor"