modernize C++: make unique

src/Mod/Spreadsheet/App/Cell.cpp

@@ -283,7 +283,7 @@ void Cell::setContent(const char * value)
         if (owner->sheet()->isRestoring()) {
             if (value[0] == '\0' || (value[0] == '\'' && value[1] == '\0'))
                 return;
-            expression.reset(new App::StringExpression(owner->sheet(), value));
+            expression = std::make_unique<App::StringExpression>(owner->sheet(), value);
             setUsed(EXPRESSION_SET, true);
             return;
         }

src/Mod/Spreadsheet/App/Sheet.cpp

@@ -675,7 +675,7 @@ void Sheet::updateProperty(CellAddress key)
             std::string s;
 
             if (cell->getStringContent(s) && !s.empty())
-                output.reset(new StringExpression(this, s));
+                output = std::make_unique<StringExpression>(this, s);
             else {
                 this->removeDynamicProperty(key.toString().c_str());
                 return;