Update mdbook to 0.4.5 to fix CVE-2020-26297
See for more details.
Thanks!
# See the License for the specific language governing permissions and
# limitations under the License.
-MDBOOK_VERSION := v0.4.3
+MDBOOK_VERSION := v0.4.5
GOLANG_VERSION := 1.13.15
PLANTUML_VERSION := 1.2020.16
GH_VERSION := 1.2.0
