improvement: handle more invalid Swagger/OpenAPI version values gracefully (#4699)

* improvement: handle more invalid version values gracefully

* use source maps in Mocha tests

yields accurate stack trace line numbers

src/core/plugins/oas3/helpers.js

@@ -2,16 +2,20 @@ import React from "react"
 
 export function isOAS3(jsSpec) {
   const oasVersion = jsSpec.get("openapi")
-  if(!oasVersion) {
+  if(typeof oasVersion !== "string") {
     return false
   }
 
-  return oasVersion.startsWith("3.0.")
+  // we gate against `3.1` becasue we want to explicitly opt into supporting it
+  // at some point in the future -- KS, 7/2018
+
+  // starts with, but is not `3.0.` exactly
+  return oasVersion.startsWith("3.0.") && oasVersion.length > 4
 }
 
 export function isSwagger2(jsSpec) {
   const swaggerVersion = jsSpec.get("swagger")
-  if(!swaggerVersion) {
+  if(typeof swaggerVersion !== "string") {
     return false
   }