Re-check custom section to allow file variable resolution (#102)

* Re-checking custom section

Re-checking the custom section after variable replacement/resolution is performed

* Updated custom variable test 

Updated test to also delete the `this.serverlessMock.variables.service.custom` value since this is being re-checked in the beforeDeploy() function now.

Author: icj217

src/index.js

@@ -51,6 +51,8 @@ class ServerlessAWSDocumentation {
   }
 
   beforeDeploy() {
+    this.customVars = this.serverless.variables.service.custom;
+    
     if (!(this.customVars && this.customVars.documentation)) return;
 
     this.cfTemplate = this.serverless.service.provider.compiledCloudFormationTemplate;

src/index.spec.js

@@ -89,6 +89,7 @@ describe('ServerlessAWSDocumentation', function () {
     });
 
     it('shouldn\'t do anything if there are no custom variables', function () {
+      delete this.serverlessMock.variables.service.custom;
       delete this.plugin.customVars;
       this.plugin.beforeDeploy();
       expect(this.serverlessMock.service.getAllFunctions).not.toHaveBeenCalled();