Update comment in scicomm.cpp (#549)

While reading this part of code I had hard time understanding the
comment, especially the misused `serious`. I tried rewording it
slightly.

src/CalcManager/CEngine/scicomm.cpp

@@ -366,7 +366,7 @@ void CCalcEngine::ProcessCommandWorker(OpCode wParam)
     {
         if (!m_bChangeOp)
         {
-            // A special goody we are doing to preserve the history, if all was done was serious of unary operations last
+            // Preserve history, if everything done before was a series of unary operations.
             CheckAndAddLastBinOpToHistory(false);
         }