gnu: ruby-hamster: Fix build.

* gnu/packages/ruby.scm (ruby-hamster)[arguments]: Run tests with ruby-2.7 and
update style.

gnu/packages/ruby.scm

@@ -3698,8 +3698,11 @@ engine.")
           "1n1lsh96vnyc1pnzyd30f9prcsclmvmkdb3nm5aahnyizyiy6lar"))))
   (build-system ruby-build-system)
   (arguments
-   '(#:phases
-     (modify-phases %standard-phases
+   (list
+    ;; Only supports Ruby 2 currently
+    #:ruby ruby-2.7
+    #:phases
+    #~(modify-phases %standard-phases
         (add-after 'unpack 'remove-unnecessary-dependencies
           (lambda _
             ;; pry is a debugging tool, and is unnecessary when running the
@@ -3711,14 +3714,12 @@ engine.")
               ;; CodeClimate is an online service, and is unnecessary for
               ;; running the tests
               (("require \"codeclimate-test-reporter\"") "")
-             (("CodeClimate.*\n") ""))
-           #t))
+              (("CodeClimate.*\n") ""))))
         ;; No Rakefile is included, so run rspec directly.
         (replace 'check
           (lambda* (#:key tests? #:allow-other-keys)
             (when tests?
-             (invoke "rspec"))
-           #t)))))
+              (invoke "ruby" (which "rspec"))))))))
   (propagated-inputs
    (list ruby-concurrent))
   (native-inputs