Update how we record Bundler versions

We rely on this information for metrics, not application logic. I
believe we're receiving poor information and making decisions based on
it. I'm updating this to see if we're indeed supporting as many Bundler
v1 projects as it seems.

bundler/lib/dependabot/bundler/helpers.rb

@@ -30,9 +30,9 @@ def self.detected_bundler_version(lockfile)
         return "unknown" unless lockfile
 
         if (matches = lockfile.content.match(BUNDLER_MAJOR_VERSION_REGEX))
-          matches[:version]
+          matches[:version].to_i
         else
-          "1"
+          "unknown"
         end
       end
     end

bundler/spec/dependabot/bundler/helper_spec.rb

@@ -76,8 +76,8 @@ def described_method(lockfile)
       expect(described_method(no_lockfile)).to eql("unknown")
     end
 
-    it "is 1 if there is no bundled with string" do
-      expect(described_method(lockfile_bundled_with_missing)).to eql("1")
+    it "is unknown if there is no bundled with string" do
+      expect(described_method(lockfile_bundled_with_missing)).to eql("unknown")
     end
 
     it "is 1 if it was bundled with a v1.x version" do
@@ -88,7 +88,7 @@ def described_method(lockfile)
       expect(described_method(lockfile_bundled_with_v2)).to eql("2")
     end
 
-    it "is 1 if it was bundled with a future version" do
+    it "reports the version if it was bundled with a future version" do
       expect(described_method(lockfile_bundled_with_future_version)).to eql("3")
     end
   end