Bump net.sf.mpxj:mpxj from 13.3.1 to 13.4.0

Bumps [net.sf.mpxj:mpxj](https://github.com/joniles/mpxj) from 13.3.1 to 13.4.0.
- [Release notes](https://github.com/joniles/mpxj/releases)
- [Changelog](https://github.com/joniles/mpxj/blob/master/CHANGELOG.md)
- [Commits](joniles/mpxj@v13.3.1...v13.4.0)

---
updated-dependencies:
- dependency-name: net.sf.mpxj:mpxj
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

biz.ganttproject.impex.msproject2/build.gradle

@@ -10,7 +10,7 @@ dependencies {
     providedCompile project(path: ':biz.ganttproject.app.libs', configuration: 'exported')
     providedCompile project(path: ':biz.ganttproject.core')
     providedCompile project(path: ':ganttproject')
-    api('net.sf.mpxj:mpxj:13.3.1') {
+    api('net.sf.mpxj:mpxj:13.4.0') {
         exclude group: 'org.xerial', module: 'sqlite-jdbc'
         exclude group: 'com.jgoodies'
     }