fillPatternStyle and fillPatternColor ignored on cells
Setting fillPatternStyle on a cell produces patternType="solid" in the output instead of the specified pattern.
```
node -e '
var w = require("write-excel-file/node")
w([[{value:"x", type:String, backgroundColor:"#ff0000", fillPatternStyle:"darkGray", fillPatternColor:"#0000ff"}]],
{filePath:"/tmp/a.xlsx"}
).then(function() {
require("child_process").execSync("unzip -o /tmp/a.xlsx -d /tmp/a >/dev/null 2>&1")
console.log(require("fs").readFileSync("/tmp/a/xl/styles.xml", "utf8").match(/patternType="[^"]+"/g))
})'
```
Actual: `patternType="none", patternType="gray125", patternType="solid"`
Expected: `patternType="none", patternType="gray125", patternType="darkGray"`
issue