Relax app.yml detection to just "runtime" (#313)

Apparently "service" is optional if you're using the default service in
the standard environment.

Fixes GH-311

Author: sethvargo

dist/index.js

@@ -292,8 +292,8 @@ export async function findAppYaml(list: string[]): Promise<string> {
       const parsed = YAML.parse(contents);
 
       // Per https://cloud.google.com/appengine/docs/standard/reference/app-yaml,
-      // the only required fields are "runtime" and "service".
-      if (parsed && parsed['runtime'] && parsed['service']) {
+      // the only required field is "runtime".
+      if (parsed && parsed['runtime']) {
         return pth;
       }
     } catch (err) {

src/main.ts

@@ -255,7 +255,6 @@ this is another file
       files: {
         'app-dev.yaml': `
 runtime: 'node'
-service: 'my-service'
       `,
       },
       expected: 'app-dev.yaml',
@@ -271,7 +270,6 @@ this is another file
       `,
         'app-prod.yaml': `
 runtime: 'node'
-service: 'my-service'
       `,
       },
       expected: 'app-prod.yaml',
@@ -286,10 +284,12 @@ service: 'my-service'
         'app-dev.yaml': `
 runtime: 'node'
 service: 'my-service'
+env: 'flex'
       `,
         'app-prod.yaml': `
 runtime: 'node'
 service: 'my-service'
+env: 'standard'
       `,
       },
       expected: 'app.yaml',