Fix typo. (From SF bug #853064)

Doc/tut/tut.tex

@@ -2146,7 +2146,7 @@ Here is a small example using a dictionary:
 True
 \end{verbatim}
 
-The \function{dict()} contructor builds dictionaries directly from
+The \function{dict()} constructor builds dictionaries directly from
 lists of key-value pairs stored as tuples.  When the pairs form a
 pattern, list comprehensions can compactly specify the key-value list.