Class names consisting of one letter are not allowed

[sjinks]

namespace Test\Calls;

class A
{
}

$ zephir fullclean; zephir generate --backend=ZendEngine3
Zephir\Parser\ParseException: Syntax error in /home/vladimir/workspace/zephir/test/calls/a.zep on line 3

at Library/CompilerFile.php(595)
#0 Library/Compiler.php(258): Zephir\CompilerFile->preCompile(Object(Zephir\Compiler))
#1 Library/Compiler.php(297): Zephir\Compiler->preCompile('test/calls/a.ze...')
#2 Library/Compiler.php(827): Zephir\Compiler->recursivePreCompile('test')
#3 Library/Commands/CommandAbstract.php(107): Zephir\Compiler->generate(Object(Zephir\Commands\CommandGenerate))
#4 Library/Bootstrap.php(200): Zephir\Commands\CommandAbstract->execute(Object(Zephir\Config), Object(Zephir\Logger))
#5 compiler.php(22): Zephir\Bootstrap::boot()
#6 {main}

At that:

namespace Test\Calls;

class a
{
}

works.