Fix REVMARK

Running a double quoted asciidoc command line as a parameter to a
docker run command line requires the asciidoc parameters to avoid
using double quotes.

Resolves: #99
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>

Author: Andrew Jones

Makefile

@@ -14,7 +14,7 @@
 
 DATE ?= $(shell date +%Y-%m-%d)
 VERSION ?= v0.9-rc3
-REVMARK ?= "This document is in development. Assume everything can change. See http://riscv.org/spec-state for details."
+REVMARK ?= 'This document is in development. Assume everything can change. See http://riscv.org/spec-state for details.'
 DOCKER_RUN := docker run --rm -v ${PWD}:/build -w /build \
 riscvintl/riscv-docs-base-container-image:latest