doc/go1.15: exclude spaces from <code> block

Per the note at the top of go1.15.html.

Updates #37419.

Change-Id: Ia6917347ca1e3ebe8c55f9c0ec74e49ff481a64f
Reviewed-on: https://go-review.googlesource.com/c/go/+/236719
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

Author: aclements

doc/go1.15.html

@@ -228,15 +228,15 @@ <h2 id="runtime">Runtime</h2>
 
 <h2 id="compiler">Compiler</h2>
 
-<p><!-- https://golang.org/cl/229578 -->
+<p><!-- CL 229578 -->
   Package <code>unsafe</code>'s <a href="/pkg/unsafe/#Pointer">safety
   rules</a> allow converting an <code>unsafe.Pointer</code>
   into <code>uintptr</code> when calling certain
   functions. Previously, in some cases, the compiler allowed multiple
-  chained conversions (for example, <code>syscall.Syscall(…,
-  uintptr(uintptr(ptr)), …)</code>). The compiler now requires exactly
-  one conversion. Code that used multiple conversions should be
-  updated to satisfy the safety rules.
+  chained conversions (for example, <code>syscall.Syscall(…,</code>
+  <code>uintptr(uintptr(ptr)),</code> <code>…)</code>). The compiler
+  now requires exactly one conversion. Code that used multiple
+  conversions should be updated to satisfy the safety rules.
 </p>
 
 <p><!-- CL 230544, CL 231397 -->