Nim: Add an explicit include for QRegExp

Other includes will be merged from 4.2. Nim doesn't exist there.

Change-Id: I0d701a07adefe04e730898a219be021ec4e70860
Reviewed-by: Samuel Gaist <samuel.gaist@edeltech.ch>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/nim/project/nimtoolchain.cpp

@@ -32,6 +32,7 @@
 
 #include <QFileInfo>
 #include <QProcess>
+#include <QRegExp>
 
 using namespace ProjectExplorer;
 using namespace Utils;