qbs build: Update minimum qbs version

Change-Id: I1af5c32f4e19f67013a53fc3da7c1bcafbd4864b
Reviewed-by: Jake Petroules <jake.petroules@qt.io>

qtcreator.qbs

@@ -4,7 +4,7 @@ import qbs.FileInfo
 
 Project {
     name: "Qt Creator"
-    minimumQbsVersion: "1.7.0"
+    minimumQbsVersion: "1.8.0"
     property string minimumMacosVersion: "10.8"
     property bool withAutotests: qbs.buildVariant === "debug"
     property path ide_source_tree: path