Use the Self keyword where applicable.

https://github.com/rust-lang-nursery/rust-clippy/wiki#use_self

lib/wasm/src/module_translator.rs

@@ -46,8 +46,8 @@ pub struct ImportMappings {
 
 impl ImportMappings {
     /// Create a new empty `ImportMappings`.
-    pub fn new() -> ImportMappings {
-        ImportMappings {
+    pub fn new() -> Self {
+        Self {
             functions: HashMap::new(),
             signatures: HashMap::new(),
         }