Fix pair source code view

Author: spolnik

src/client/problems/components/SourceCode.tsx

@@ -104,6 +104,11 @@ const PairSourceCode = (props: SourceCodeProps) => (
         sourceCode={`public class Pair {
     public Object first;
     public Object second;
+
+    public Pair(Object first, Object second) {
+        this.first = first;
+        this.second = second;
+    }
 }`}
         show={props.show}
         onHide={props.onHide}