LanguageClient: Fix build for older compiler

Amends ed77e10571.

Change-Id: Icd41c65ae308f8862cd9b11ac32f8f8d22e7f6e3
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/languageclient/languageclientsettings.cpp

@@ -538,11 +538,11 @@ public:
         if (result.size() == 1) {
             switch (result.at(0).toLatin1()) {
             case '\n':
-                return "\\n";
+                return QString("\\n");
             case '\t':
-                return "\\t";
+                return QString("\\t");
             case '\r':
-                return "\\r";
+                return QString("\\r");
             }
         }
         return result;