Update wast to 7.0.0, fix stack overflow (#897)

This updates the `wast` dependency to include bytecodealliance/wat#48
which fixes a stack overflow for deeply recursive `*.wat` files.

crates/wast/Cargo.toml

@@ -13,7 +13,7 @@ edition = "2018"
 [dependencies]
 anyhow = "1.0.19"
 wasmtime = { path = "../api", version = "0.9.0" }
-wast = "6.0.0"
+wast = "7.0.0"
 
 [badges]
 maintenance = { status = "actively-developed" }

crates/wast/src/wast.rs

@@ -339,7 +339,6 @@ impl WastContext {
                     )
                 }
             }
-            AssertReturnFunc { .. } => bail!("need to implement assert_return_func"),
         }
 
         Ok(())