docs(pipes): typo in pure pipe chapter - "is is" - "it is" (#3180)

Author: wingsuitist

public/docs/ts/latest/guide/pipes.jade

@@ -295,7 +295,7 @@ block pure-change
   Angular ignores changes *within* (composite) objects.
   It won't call a pure pipe if we change an input month, add to an input #{_array}, or update an input object property.
 
-  This may seem restrictive but is is also fast.
+  This may seem restrictive but it is also fast.
   An object reference check is fast — much faster than a deep check for
   differences — so Angular can quickly determine if it can skip both the
   pipe execution and a view update.