feat(bunder): extract ruby compatibiity version

lib/manager/bundler/extract.js

@@ -16,6 +16,10 @@ function extractPackageFile(content) {
     if (sourceMatch) {
       res.registryUrls.push(sourceMatch[1]);
     }
+    const rubyMatch = line.match(/^ruby "([^"]+)"/);
+    if (rubyMatch) {
+      res.compatibility = { ruby: rubyMatch[1] };
+    }
     const gemMatch = line.match(/^gem "([^"]+)"(,\s+"([^"]+)"){0,2}/);
     if (gemMatch) {
       const dep = {

test/_fixtures/bundler/Gemfile.sourceGroup

 source "https://rubygems.org"
+ruby "~> 1.5.3"
 
 source "https://gems.example.com" do
   gem "some_internal_gem"

test/manager/bundler/__snapshots__/extract.spec.js.snap

@@ -499,10 +499,13 @@ Object {
 
 exports[`lib/manager/bundler/extract extractPackageFile() parses sourceGroups 1`] = `
 Object {
+  "compatibility": Object {
+    "ruby": "~> 1.5.3",
+  },
   "deps": Array [
     Object {
       "depName": "some_internal_gem",
-      "lineNumber": 3,
+      "lineNumber": 4,
       "registryUrls": Array [
         "https://gems.example.com",
       ],
@@ -510,7 +513,7 @@ Object {
     },
     Object {
       "depName": "another_internal_gem",
-      "lineNumber": 4,
+      "lineNumber": 5,
       "registryUrls": Array [
         "https://gems.example.com",
       ],
@@ -519,12 +522,12 @@ Object {
     Object {
       "currentValue": "latest",
       "depName": "ruby-debug",
-      "lineNumber": 8,
+      "lineNumber": 9,
       "skipReason": "invalid-value",
     },
     Object {
       "depName": "sqlite3",
-      "lineNumber": 9,
+      "lineNumber": 10,
       "skipReason": "no-version",
     },
     Object {
@@ -533,7 +536,7 @@ Object {
         "development",
         "optional => true",
       ],
-      "lineNumber": 13,
+      "lineNumber": 14,
       "skipReason": "no-version",
     },
     Object {
@@ -542,7 +545,7 @@ Object {
         "development",
         "optional => true",
       ],
-      "lineNumber": 14,
+      "lineNumber": 15,
       "skipReason": "no-version",
     },
   ],