Get Julia versions from versions.json (#24)

This replaces the hardcoded versions array which will decouple the setup-julia version and the installable Julia versions.

package-lock.json

@@ -5461,6 +5461,36 @@
       "integrity": "sha512-1nh45deeb5olNY7eX82BkPO7SSxR5SSYJiPTrTdFUVYwAl8CKMA5N9PjTYkHiRjisVcxcQ1HXdLhx2qxxJzLNQ==",
       "dev": true
     },
+    "nock": {
+      "version": "11.7.2",
+      "resolved": "https://registry.npmjs.org/nock/-/nock-11.7.2.tgz",
+      "integrity": "sha512-7swr5bL1xBZ5FctyubjxEVySXOSebyqcL7Vy1bx1nS9IUqQWj81cmKjVKJLr8fHhtzI1MV8nyCdENA/cGcY1+Q==",
+      "dev": true,
+      "requires": {
+        "debug": "^4.1.0",
+        "json-stringify-safe": "^5.0.1",
+        "lodash": "^4.17.13",
+        "mkdirp": "^0.5.0",
+        "propagate": "^2.0.0"
+      },
+      "dependencies": {
+        "debug": {
+          "version": "4.1.1",
+          "resolved": "https://registry.npmjs.org/debug/-/debug-4.1.1.tgz",
+          "integrity": "sha512-pYAIzeRo8J6KPEaJ0VWOh5Pzkbw/RetuzehGM7QRRX5he4fPHx2rdKMB256ehJCkX+XRQm16eZLqLNS8RSZXZw==",
+          "dev": true,
+          "requires": {
+            "ms": "^2.1.1"
+          }
+        },
+        "ms": {
+          "version": "2.1.2",
+          "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.2.tgz",
+          "integrity": "sha512-sGkPx+VjMtmA6MX27oA4FBFELFCZZ4S4XqeGOXCv68tT+jb3vk/RyaKWP0PTKyWtmLSM0b+adUTEvbs1PEaH2w==",
+          "dev": true
+        }
+      }
+    },
     "node-int64": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/node-int64/-/node-int64-0.4.0.tgz",
@@ -5821,6 +5851,12 @@
         "sisteransi": "^1.0.4"
       }
     },
+    "propagate": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/propagate/-/propagate-2.0.1.tgz",
+      "integrity": "sha512-vGrhOavPSTz4QVNuBNdcNXePNdNMaO1xj9yBeH1ScQPjk/rhg9sSlCXPhMkFuaNNW/syTvYqsnbIJxMBfRbbag==",
+      "dev": true
+    },
     "psl": {
       "version": "1.7.0",
       "resolved": "https://registry.npmjs.org/psl/-/psl-1.7.0.tgz",