doc: use HTTPS for clang.llvm.org link in go1.6.html

Change-Id: I67aac387359378cf7aa8f7cafa6557ebf1338baf
Reviewed-on: https://go-review.googlesource.com/118176Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.6.html

@@ -116,7 +116,7 @@ instead of generated from <a href="/cmd/yacc/">yacc</a>.
 <p>
 The compiler, linker, and <code>go</code> command have a new flag <code>-msan</code>,
 analogous to <code>-race</code> and only available on linux/amd64,
-that enables interoperation with the <a href="http://clang.llvm.org/docs/MemorySanitizer.html">Clang MemorySanitizer</a>.
+that enables interoperation with the <a href="https://clang.llvm.org/docs/MemorySanitizer.html">Clang MemorySanitizer</a>.
 Such interoperation is useful mainly for testing a program containing suspect C or C++ code.
 </p>