JavaRequirement: fix version parsing to handle Java 9 and higher

Library/Homebrew/requirements/java_requirement.rb

@@ -26,7 +26,7 @@ class JavaRequirement < Requirement
   end
 
   def initialize(tags = [])
-    @version = tags.shift if /(\d+\.)+\d/ =~ tags.first
+    @version = tags.shift if /^\d/ =~ tags.first
     super(tags)
   end
 

Library/Homebrew/test/requirements/java_requirement_spec.rb

@@ -0,0 +1,30 @@
+require "requirements/java_requirement"
+
+describe JavaRequirement do
+  describe "initialize" do
+    it "parses '1.8' tag correctly" do
+      req = described_class.new(["1.8"])
+      expect(req.display_s).to eq("java = 1.8")
+    end
+
+    it "parses '9' tag correctly" do
+      req = described_class.new(["9"])
+      expect(req.display_s).to eq("java = 9")
+    end
+
+    it "parses '9+' tag correctly" do
+      req = described_class.new(["9+"])
+      expect(req.display_s).to eq("java >= 9")
+    end
+
+    it "parses '11' tag correctly" do
+      req = described_class.new(["11"])
+      expect(req.display_s).to eq("java = 11")
+    end
+
+    it "parses bogus tag correctly" do
+      req = described_class.new(["bogus1.8"])
+      expect(req.display_s).to eq("java")
+    end
+  end
+end