fix: Replace AMO API v3 with v4 (#2121)

Only src/program.js needs to be changed, but I replaced all instances of
v3 with v4 to minimize confusion.

Author: Rob--W

CONTRIBUTING.md

@@ -312,7 +312,7 @@ so as not to disturb any real `addons.mozilla.org` data.
 
   ````
   web-ext sign --api-key user:123 --api-secret abc1234 \
-      --api-url-prefix https://addons-dev.allizom.org/api/v3
+      --api-url-prefix https://addons-dev.allizom.org/api/v4
   ````
 * Signed add-ons created with the development API are hard to install into
   Firefox. If you need to test installation of add-ons (you probably don't)

src/program.js

@@ -527,7 +527,7 @@ Example: $0 --help run.
         },
         'api-url-prefix': {
           describe: 'Signing API URL prefix',
-          default: 'https://addons.mozilla.org/api/v3',
+          default: 'https://addons.mozilla.org/api/v4',
           demandOption: true,
           type: 'string',
         },

tests/functional/test.cli.sign.js

@@ -54,7 +54,7 @@ describe('web-ext sign', () => {
      () => withTempAddonDir({addonPath: minimalAddonPath}, (srcDir, tmpDir) => {
        const argv = [
          'sign', '--verbose',
-         '--api-url-prefix', 'http://localhost:8989/fake/api/v3',
+         '--api-url-prefix', 'http://localhost:8989/fake/api/v4',
          '--api-key', 'FAKEAPIKEY', '--api-secret', 'FAKEAPISECRET',
          '--source-dir', srcDir,
        ];
@@ -85,7 +85,7 @@ describe('web-ext sign', () => {
          JSON.stringify({
            webExt: {
              sign: {
-               apiUrlPrefix: 'http://localhost:8989/fake/api/v3',
+               apiUrlPrefix: 'http://localhost:8989/fake/api/v4',
              },
              sourceDir: srcDir,
            },

tests/unit/test-cmd/test.sign.js

@@ -29,7 +29,7 @@ describe('sign', () => {
     const signingConfig = {
       apiKey: 'AMO JWT issuer',
       apiSecret: 'AMO JWT secret',
-      apiUrlPrefix: 'http://not-the-real-amo.com/api/v3',
+      apiUrlPrefix: 'http://not-the-real-amo.com/api/v4',
       apiProxy: 'http://yourproxy:6000',
       timeout: 999,
     };