Fixed expansion of _FALSE binary expression

- see #1051

include/internal/catch_assertionresult.cpp

@@ -54,8 +54,8 @@ namespace Catch {
     }
 
     std::string AssertionResult::getExpression() const {
-        if (isFalseTest(m_info.resultDisposition))
-            return '!' + std::string(m_info.capturedExpression);
+        if( isFalseTest( m_info.resultDisposition ) )
+            return "!(" + std::string(m_info.capturedExpression) + ")";
         else
             return m_info.capturedExpression;
     }