Work around invalid version numbers in the r-builds version list

NEWS.md

@@ -1,4 +1,8 @@
 
+# 2.3.7
+
+* Work around invalid version numbers in the r-builds version list.
+
 # 2.3.6
 
 * Add support for retired distros for which we have binaries.

lib/linux-builds-amd64.js

@@ -1,4 +1,5 @@
 
+const semver = require('semver');
 const mycache = require('./cache');
 const urls = require('./urls');
 
@@ -10,7 +11,10 @@ async function linux_builds_amd64(cache = true) {
     if (cached !== undefined) { return cached; }
 
     var resp = await got(urls.linux_builds_amd64).json();
-    const value = resp.r_versions;
+    var value = resp.r_versions;
+    value = value.filter(function(x) {
+	return !!semver.valid(x) || x == 'next' || x == 'devel'
+    });
 
     mycache.set('linux_builds_amd64', value);
     return value;

package.json

@@ -1,6 +1,6 @@
 {
   "name": "rversions",
-  "version": "2.3.6",
+  "version": "2.3.7",
   "description": "Query the current and past R versions",
   "main": "index.js",
   "scripts": {