fix: sol_interface! macro with no arguments

[evmcheb]

I think sol_interface! is broken if you pass in no arguments due to a leading comma

sol_interface! {
    interface A {
        function B() view returns (address);
    }
}
error: expected type, found `,`
  --> src/main.rs:22:1
   |
22 | / sol_interface! {
23 | |     interface A {
24 | |         function B() view returns (address);
25 | |     }
26 | | }
   | |_^ expected type
   |

This change to the macro should fix it (untested, I couldn't get a testing environment to work)

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[hkalodner]

Hey @evmcheb, thanks for the contribution! Just bumping are you ok with signing the contributor agreement? Would love to get a fix for this issue merged in 🙏

[rachel-bousfield]

Thanks for the PR! We went ahead and solved this along with another fix in the following PR that'll be included in the v0.2.0 release

• Fix sol_interface! when expanding empty args #48