Fix typos in extractor-objects.md (scala#1040)

Provide consistent punctuation

Author: Gommorach

_tour/extractor-objects.md

@@ -53,8 +53,8 @@ val CustomerID(name2) = "--asdfasdfasdf"
 
 The return type of an `unapply` should be chosen as follows:
 
-* If it is just a test, return a `Boolean`. For instance `case even()`
-* If it returns a single sub-value of type T, return an `Option[T]`
+* If it is just a test, return a `Boolean`. For instance `case even()`.
+* If it returns a single sub-value of type T, return an `Option[T]`.
 * If you want to return several sub-values `T1,...,Tn`, group them in an optional tuple `Option[(T1,...,Tn)]`.
 
 Sometimes, the number of sub-values isn't fixed and we would like to return a sequence. For this reason, you can also define patterns through `unapplySeq` which returns `Option[Seq[T]]` This mechanism is used for instance in pattern `case List(x1, ..., xn)`.