Simplify fit addon

src/addons/fit/fit.ts

@@ -50,11 +50,6 @@ export function fit(term) {
 };
 
 export function apply(terminalConstructor) {
-  terminalConstructor.prototype.proposeGeometry = function () {
-    return proposeGeometry(this);
-  };
-
-  terminalConstructor.prototype.fit = function () {
-    return fit(this);
-  };
+  terminalConstructor.prototype.proposeGeometry = proposeGeometry.bind(this, this);
+  terminalConstructor.prototype.fit = fit.bind(this, this);
 }