2016/prototype-your-design: Fix typo

Change-Id: I5bd6c44d94337d0d4f89a2af785c504c872baf41
Reviewed-on: https://go-review.googlesource.com/33302
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

2016/prototype-your-design.txt

diff --git a/2016/prototype-your-design.txt b/2016/prototype-your-design.txt
index e791497..0fd6454 100644
--- a/2016/prototype-your-design.txt
+++ b/2016/prototype-your-design.txt
@@ -45,7 +45,7 @@
 So how can we get around this notation problem? There are a few solutions:
 1) We can say it’s not a problem - and some people will be ok with this.
 2) We can actually change the Go language for the experiment; but that is likely way too costly.
-3) Or, we could rewrite the source: Whenever we see say a[i, j], we change it into a method call a.At(i, j). Basically what the gonum folks are doing now, expect they don’t start with the nice notation.
+3) Or, we could rewrite the source: Whenever we see say a[i, j], we change it into a method call a.At(i, j). Basically what the gonum folks are doing now, except they don’t start with the nice notation.
 Ideally we want to have a tool, a source-to-source rewriter that does this for us.
 
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