lang: Fix detection of Accounts derive

[tomlinton]

The following snippet breaks the IDL parser due to the presence of Accounts in the outer doc comment which leads the IDL parser to think it is an Accounts derive.

/// Accounts in context of initialize_vault instruction
#[account]
#[derive(Default)]
pub struct VaultInfo {
    pub token_a: Pubkey,
    pub token_b: Pubkey,
    pub vault_name: [u8; 20],
}