Consistently include a trailing slash in the API root URL

Some API URLs are created by resolving relative URLs against the API
root. For this to work properly, the root URL has to include a trailing
slash.

The omission of this in the documentation caused confusion for eLife
devs.

docs/publishers/config.rst

@@ -102,7 +102,7 @@ loads.
       window.hypothesisConfig = function () {
         return {
           services: [{
-            apiUrl: 'https://hypothes.is/api',
+            apiUrl: 'https://hypothes.is/api/',
             authority: 'partner.org',
             grantToken: '***',
             icon: 'https://openclipart.org/download/272629/sihouette-animaux-10.svg'

src/sidebar/test/host-config-test.js

@@ -39,7 +39,7 @@ describe('hostPageConfig', function () {
 
   it('ignores non-whitelisted config params', function () {
     var window_ = fakeWindow({
-      apiUrl: 'https://not-the-hypothesis/api',
+      apiUrl: 'https://not-the-hypothesis/api/',
     });
 
     assert.deepEqual(hostPageConfig(window_), {});

src/sidebar/test/store-test.js

@@ -29,7 +29,7 @@ describe('store', function () {
 
     angular.mock.module('h', {
       auth: fakeAuth,
-      settings: {apiUrl: 'http://example.com/api'},
+      settings: {apiUrl: 'http://example.com/api/'},
     });
 
     angular.mock.inject(function (_$q_) {
@@ -50,7 +50,7 @@ describe('store', function () {
     $httpBackend = _$httpBackend_;
     store = _store_;
 
-    $httpBackend.expectGET('http://example.com/api').respond({
+    $httpBackend.expectGET('http://example.com/api/').respond({
       // Return an API route directory.
       // This should mirror the structure (but not the exact URLs) of
       // https://hypothes.is/api/.