_content/doc/go1.18: change some 1.19 references to "a future release"

Realistically many of these changes are not going to happen in 1.19,
since the freeze is only five weeks away. If they get in, great.
But let's not suggest that that is likely.

Change-Id: Icd8478d10bc8657838fd196fb1157204c7a9b629
Reviewed-on: https://go-review.googlesource.com/c/website/+/394254
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Trust: Ian Lance Taylor <iant@google.com>
diff --git a/_content/doc/go1.18.html b/_content/doc/go1.18.html
index 9ec7fd3..c9be609 100644
--- a/_content/doc/go1.18.html
+++ b/_content/doc/go1.18.html
@@ -150,12 +150,13 @@
   <ul>
     <li><!-- https://golang.org/issue/47631 -->
       The Go compiler cannot handle type declarations inside generic functions
-      or methods. We hope to provide support for this feature in Go 1.19.
+      or methods. We hope to provide support for this feature in a
+      future release.
     </li>
     <li><!-- https://golang.org/issue/50937 -->
       The Go compiler does not accept arguments of type parameter type with
       the predeclared functions <code>real</code>, <code>imag</code>, and <code>complex</code>.
-      We hope to remove this restriction in Go 1.19.
+      We hope to remove this restriction in a future release.
     </li>
     <li><!-- https://golang.org/issue/51183 -->
       The Go compiler only supports calling a method <code>m</code> on a value
@@ -165,13 +166,14 @@
       <code>P.m</code> also are only supported if <code>m</code> is explicitly
       declared by <code>P</code>, even though <code>m</code> might be in the method set
       of <code>P</code> by virtue of the fact that all types in <code>P</code> implement
-      <code>m</code>. We hope to remove this restriction in Go 1.19.
+      <code>m</code>. We hope to remove this restriction in a future
+      release.
     </li>
     <li><!-- https://golang.org/issue/51576 -->
       The Go compiler does not support accessing a struct field <code>x.f</code>
       where <code>x</code> is of type parameter type even if all types in the
       type parameter's type set have a field <code>f</code>.
-      We may remove this restriction in Go 1.19.
+      We may remove this restriction in a future release.
     </li>
     <li><!-- https://golang.org/issue/49030 -->
       Embedding a type parameter, or a pointer to a type parameter, as
@@ -596,7 +598,7 @@
   Because of changes in the compiler related to supporting generics, the
   Go 1.18 compile speed can be roughly 15% slower than the Go 1.17 compile speed.
   The execution time of the compiled code is not affected.  We
-  intend to improve the speed of the compiler in Go 1.19.
+  intend to improve the speed of the compiler in future releases.
 </p>
 
 <h2 id="linker">Linker</h2>