Fix jruby-9.1.x compatibility (#79)

* Run tests against jruby-9.1.12.0

* Fix compatibility

* Run tests against latest jruby-9.1.x version

* Add jruby 9.2 for good measure

Co-authored-by: Thomas Hu <thomasrockhu@users.noreply.github.com>

Author: mainameiz

.travis.yml

@@ -9,3 +9,5 @@ rvm:
   - 2.6
   - 2.7
   - jruby
+  - jruby-9.1
+  - jruby-9.2

lib/codecov.rb

@@ -315,10 +315,12 @@ def create_report(report)
   def gzip_report(report)
     puts ['==>'.green, 'Gzipping contents'].join(' ')
 
-    gzip = Zlib::GzipWriter.new(StringIO.new)
+    io = StringIO.new
+    gzip = Zlib::GzipWriter.new(io)
     gzip << report
+    gzip.close
 
-    gzip.close.string
+    io.string
   end
 
   def upload_to_codecov(ci, report)