Try to get more information calling composer update -v to get a list of possible version strings you can use.
I for example got the info, that the correct name for fetching the trunk was this config:
{
"name": "sample/test",
"type": "library",
"version": "0.0.0",
"time" : "2013-04-16",
"description": "Testing ...",
"repositories": [
{
"type": "svn",
"url": "http://framework.zend.com/svn/framework/standard"
}
],
"require": {
"php": ">=5.3.3",
"zendframework/zendframework1" : "dev-trunk"
}
}
Calling composer with -v as argument, you'll get a list of branches, tags and the trunk, if found. I don't know if false is allowed as path for tags and branches ...
$ composer update -v
Loading composer repositories with package information
Reading composer.json of zendframework/zendframework1 (release-0.1.1)
Skipped tag 0.1.1, no composer file was found
Reading composer.json of zendframework/zendframework1 (release-0.1.2)
Skipped tag 0.1.2, no composer file was found
Reading composer.json of zendframework/zendframework1 (release-0.1.3)
Skipped tag 0.1.3, no composer file was found
....
Reading composer.json of zendframework/zendframework1 (release-1.9.6)
Importing tag 1.9.6 (1.9.6.0)
Reading composer.json of zendframework/zendframework1 (release-1.9.7)
Importing tag 1.9.7 (1.9.7.0)
Reading composer.json of zendframework/zendframework1 (release-1.9.8)
Importing tag 1.9.8 (1.9.8.0)
Reading composer.json of zendframework/zendframework1 (trunk)
Importing branch trunk (dev-trunk)
Reading composer.json of zendframework/zendframework1 (bughuntday)
Skipped branch bughuntday, no composer file was found
Reading composer.json of zendframework/zendframework1 (development-2.0)
Skipped branch development-2.0, no composer file was found
Reading composer.json of zendframework/zendframework1 (pdo_ibm_ids_support)
Skipped branch pdo_ibm_ids_support, no composer file was found
Reading composer.json of zendframework/zendframework1 (release-1.0)
Importing branch release-1.0 (dev-release-1.0)
Reading composer.json of zendframework/zendframework1 (release-1.10)
Importing branch release-1.10 (dev-release-1.10)
....
Reading composer.json of zendframework/zendframework1 (release-1.8)
Importing branch release-1.8 (dev-release-1.8)
Reading composer.json of zendframework/zendframework1 (release-1.9)
Importing branch release-1.9 (dev-release-1.9)
Reading composer.json of zendframework/zendframework1 (rob_allen)
Skipped branch rob_allen, no composer file was found
Reading composer.json of zendframework/zendframework1 (user)
Skipped branch user, no composer file was found
Updating dependencies (including require-dev)
You can safely ignore all excepted by this line, which tells you what you have to set as requested version:
Importing branch trunk (dev-trunk)