QbsProjectManager: Fix document filtering

This was broken in 929083e7b6.

Change-Id: I5341a90bf8067d93485a75827309840b5212d2b4
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/qbsprojectmanager/qbsproject.cpp

@@ -738,9 +738,8 @@ void QbsProject::updateDocuments(const std::set<QString> &files)
     const FilePath buildDir = FilePath::fromString(m_projectData.buildDirectory());
     const QVector<FilePath> nonBuildDirFilePaths = filtered(filePaths,
                                                             [buildDir](const FilePath &p) {
-                                                                return p.isChildOf(buildDir);
+                                                                return !p.isChildOf(buildDir);
                                                             });
-
     setExtraProjectFiles(nonBuildDirFilePaths);
 }