Replace single_file by allow_single_file (#13)

* Replace `single_file` by `allow_single_file`

Fix #12

* Replace http:// by https:// for third_party resources.

ERROR: /tmp/cirrus-ci-build/third_party/com/google/guava/BUILD:7:1: //third_party/com/google/guava:guava depends on @com_google_guava_guava_26_0_jre//jar:jar in repository @com_google_guava_guava_26_0_jre which failed to fetch. no such package '@com_google_guava_guava_26_0_jre//jar': Plain HTTP URLs are not allowed without checksums in the maven_jar rule. Please use HTTPS for the maven_server rule for http://jcenter.bintray.com/ or add a sha1 checksum to the maven_jar rule. To disable this check, pass --incompatible_disallow_unverified_http_downloads=false to your build
ERROR: Analysis of target '//third_party/com/google/guava:guava' failed; build aborted: Analysis failed

cup/cup.bzl

@@ -42,8 +42,7 @@ cup = rule(
     implementation = _cup_impl,
     attrs = {
         "src": attr.label(
-            allow_files = True,
-            single_file = True,
+            allow_single_file = True,
             mandatory = True,
             doc = "The CUP grammar specification",
         ),

jflex/jflex.bzl

@@ -45,8 +45,7 @@ jflex = rule(
             doc = "a list of grammar specifications",
         ),
         "skeleton": attr.label(
-            allow_files = True,
-            single_file = True,
+            allow_single_file = True,
             doc = "an optional skeleton",
         ),
         "outputs": attr.output_list(allow_empty = False),

third_party/third_party_deps.bzl

@@ -4,10 +4,10 @@ def third_party_deps():
     native.maven_jar(
         name = "com_google_guava_guava_26_0_jre",
         artifact = "com.google.guava:guava:26.0-jre",
-        repository = "http://jcenter.bintray.com/",
+        repository = "https://jcenter.bintray.com/",
     )
     native.maven_jar(
         name = "com_google_truth_truth",
         artifact = "com.google.truth:truth:0.42",
-        repository = "http://jcenter.bintray.com/",
+        repository = "https://jcenter.bintray.com/",
     )