sol-compiler constructor argument cannot be undefined

[frangio]

The Compiler constructor is typed and documented with an optional argument, but there's actually a runtime validation that doesn't allow omitting it.

0x-monorepo/packages/sol-compiler/src/compiler.ts

Lines 98 to 99 in a50eefc

	constructor(opts?: CompilerOptions) {
	assert.doesConformToSchema('opts', opts, compilerOptionsSchema);

> const compiler = new Compiler()
Error: opts can't be undefined
    at Object.doesConformToSchema (/home/frangio/zs/oz/docgen/node_modules/@0x/assert/lib/src/index.js:55:19)
    at new Compiler (/home/frangio/zs/oz/docgen/node_modules/@0x/sol-compiler/lib/src/compiler.js:126:25)
    at repl:1
    at Script.runInThisContext (vm.js:123:20)
    at REPLServer.defaultEval (repl.js:332:29)
    at bound (domain.js:393:14)
    at REPLServer.runBound [as eval] (domain.js:406:12)