Fix initial Git cloning

At least on Git Bash on Windows, the existing incantations would result in

git clone ' --depth 1' --verbose https://github.com/whatwg/html.git /c/src/html-build/html

which would fail with "too many arguments". The new version results in

git clone --depth=1 --verbose https://github.com/whatwg/html.git /c/src/html-build/html

which works.

build.sh

@@ -25,7 +25,7 @@ HTML_SOURCE=${HTML_SOURCE:-}
 HTML_CACHE=${HTML_CACHE:-$DIR/.cache}
 HTML_TEMP=${HTML_TEMP:-$DIR/.temp}
 HTML_OUTPUT=${HTML_OUTPUT:-$DIR/output}
-HTML_GIT_CLONE_OPTIONS=${HTML_GIT_CLONE_OPTIONS:-"--depth 1"}
+HTML_GIT_CLONE_OPTIONS=${HTML_GIT_CLONE_OPTIONS:-"--depth=1"}
 
 # These are used by child scripts, and so we export them
 export HTML_CACHE