[FIX] owl: add prettier to devDependencies

also, run prettier on codebase

closes #498

tests/qweb/qweb.test.ts

@@ -1225,7 +1225,10 @@ describe("t-on", () => {
     );
     const steps: string[] = [];
     const owner = {
-      projects: [{ id: 1, name: "Project 1" }, { id: 2, name: "Project 2" }],
+      projects: [
+        { id: 1, name: "Project 1" },
+        { id: 2, name: "Project 2" }
+      ],
 
       onEdit(projectId, ev) {
         expect(ev.defaultPrevented).toBe(true);

tests/qweb/qweb_expressions.test.ts

@@ -27,7 +27,10 @@ describe("tokenizer", () => {
       { type: "VALUE", value: "2" },
       { type: "RIGHT_BRACE", value: "}" }
     ]);
-    expect(tokenize("a,")).toEqual([{ type: "SYMBOL", value: "a" }, { type: "COMMA", value: "," }]);
+    expect(tokenize("a,")).toEqual([
+      { type: "SYMBOL", value: "a" },
+      { type: "COMMA", value: "," }
+    ]);
     expect(tokenize("][")).toEqual([
       { type: "RIGHT_BRACKET", value: "]" },
       { type: "LEFT_BRACKET", value: "[" }