travisify: make sure build.sh is committed as executable on Windows

[imagejan]

When running travisify.sh on Windows (Git Bash), the committed build.sh script is not executable. Apparently, setting with chmod isn't sufficient on Windows:

scijava-scripts/travisify.sh

Line 137 in 818b971

chmod +x "$tmpFile"

In my experience, using git update-index is required:

git update-index --chmod=+x .travis/build.sh

My bash scripting skills are limited, so I was unsure where to add this line, but think it would likely belong into the update() function:

scijava-scripts/travisify.sh

Lines 41 to 63 in 818b971

	update() {
	file=$1
	msg=$2
	test "$msg" || msg="Travis: update $file"
	if [ -e "$file" ]
	then
	if diff -q "$file" "$tmpFile" >/dev/null
	then
	info "$file is already OK"
	else
	info "Updating $file"
	$EXEC rm -rf "$file"
	$EXEC mv -f "$tmpFile" "$file"
	fi
	else
	info "Creating $file"
	$EXEC mkdir -p "$(dirname "$file")"
	$EXEC mv "$tmpFile" "$file"
	fi
	rm -rf "$tmpFile"
	$EXEC git add "$file"
	$EXEC git diff-index --quiet HEAD -- || $EXEC git commit -m "$msg"
	}

[ctrueden]

@imagejan If you ever find yourself Travisifying anything again on Windows, feel free to add the git update-index --chmod=+x .travis/build.sh line to the script yourself where it might work, run the script, and see how it goes? I don't regularly use Windows, but I could at least test that the addition of such a line doesn't break anything on macOS or Linux.