[release] Bump version to 0.6.pre13.

INSTALL.txt

@@ -12,8 +12,8 @@ Quick Start
 
 If you haven't already done so, extract the tarball:
 
-    tar -x --xz < oil-0.6.pre12.tar.xz
-    cd oil-0.6.pre12
+    tar -x --xz < oil-0.6.pre13.tar.xz
+    cd oil-0.6.pre13
 
 Either install as /usr/local/bin/osh:
 
@@ -31,7 +31,7 @@ The latter doesn't require root access, but it requires ~/bin to be in your
 PATH.
 
 NOTE: Out-of-tree builds are NOT currently supported, so you have to be in the
-oil-0.6.pre12 directory.
+oil-0.6.pre13 directory.
 
 Smoke Test
 ----------

doc/osh-quick-ref-toc.txt

@@ -2,7 +2,7 @@ OSH Quick Reference
 
 - Below is a list of topics, organized into [Sections].
 - The X prefix means "unimplemented".  Oil features are all unimplemented!
-- HTML version: https://www.oilshell.org/release/0.6.pre12/doc/osh-quick-ref.html
+- HTML version: https://www.oilshell.org/release/0.6.pre13/doc/osh-quick-ref.html
 
 INTRO
   [Overview]      overview   osh-vs-oil   command-vs-expr

doc/release-index.md

@@ -1,6 +1,6 @@
 <!-- NOTE: This file is at /release/$VERSION/index.html -->
 
-Oil Version 0.6.pre12
+Oil Version 0.6.pre13
 -----------------
 
 ### What's New

oil-version.txt

@@ -1,4 +1,4 @@
-0.6.pre12
+0.6.pre13
 
 # The first line of this file is the Oil version, and the rest is ignored.
 # It's used at build time for the release tarball, and at runtime for oil