[ci] Bump version for development (#4730)

* Update _pkgdown.yml

* Update .appveyor.yml

* Update VERSION.txt

* Auto-update configure
Co-authored-by: GitHub Actions Bot <githubactionsbot@users.noreply.github.com>

.appveyor.yml

-version: 3.3.1.{build}
+version: 3.3.1.99.{build}
 
 image: Visual Studio 2015
 platform: x64

R-package/configure

 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.69 for lightgbm 3.3.1.
+# Generated by GNU Autoconf 2.69 for lightgbm 3.3.1.99.
 #
 #
 # Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
@@ -576,8 +576,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='lightgbm'
 PACKAGE_TARNAME='lightgbm'
-PACKAGE_VERSION='3.3.1'
-PACKAGE_STRING='lightgbm 3.3.1'
+PACKAGE_VERSION='3.3.1.99'
+PACKAGE_STRING='lightgbm 3.3.1.99'
 PACKAGE_BUGREPORT=''
 PACKAGE_URL=''
 
@@ -1182,7 +1182,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures lightgbm 3.3.1 to adapt to many kinds of systems.
+\`configure' configures lightgbm 3.3.1.99 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1244,7 +1244,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of lightgbm 3.3.1:";;
+     short | recursive ) echo "Configuration of lightgbm 3.3.1.99:";;
    esac
   cat <<\_ACEOF
 
@@ -1311,7 +1311,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-lightgbm configure 3.3.1
+lightgbm configure 3.3.1.99
 generated by GNU Autoconf 2.69
 
 Copyright (C) 2012 Free Software Foundation, Inc.
@@ -1328,7 +1328,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by lightgbm $as_me 3.3.1, which was
+It was created by lightgbm $as_me 3.3.1.99, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   $ $0 $@
@@ -2398,7 +2398,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by lightgbm $as_me 3.3.1, which was
+This file was extended by lightgbm $as_me 3.3.1.99, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -2451,7 +2451,7 @@ _ACEOF
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config="`$as_echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`"
 ac_cs_version="\\
-lightgbm config.status 3.3.1
+lightgbm config.status 3.3.1.99
 configured by $0, generated by GNU Autoconf 2.69,
   with options \\"\$ac_cs_config\\"
 

R-package/pkgdown/_pkgdown.yml

@@ -14,7 +14,7 @@ repo:
     user: https://github.com/
 
 development:
-  mode: release
+  mode: unreleased
 
 authors:
   Yu Shi:

VERSION.txt

-3.3.1
+3.3.1.99