ci: remove Travis (#914)

Summary:
Closes #902. CircleCI continues to work fast and well, on both the
commit and nightly workflows. Travis continues to be slower. It is time.

I have disabled Travis for `sourcecred/sourcecred` via:
<https://travis-ci.org/profile/sourcecred>

This commit removes the vestigial configuration files and code.

Test Plan:
Running `yarn test` still works. Running `yarn test --full` still works,
and properly invokes `sharness-full` and the various extra tests.
Running `git grep -i travis` yields no results.

wchargin-branch: ci-remove-travis

.travis.yml

@@ -1,10 +0,0 @@
-language: node_js
-node_js:
-  - "8"
-script: yarn test
-notifications:
-  email:
-    recipients:
-      - wchargin+travis-sourcecred@gmail.com
-      - decentralion+travis-sourcecred@dandelion.io
-    on_failure: always

CONTRIBUTING.md

@@ -117,7 +117,7 @@ to run them all. This will run:
     can take advantage of this to insert a quick hack and make sure that
     you remember to remove it later.
 
-This is the same set of tests that is run on our CI system, Travis.
+This is the same set of tests that is run on our CI system, CircleCI.
 
 ### Updating CHANGELOG.md
 

config/test.js

@@ -7,11 +7,7 @@ const execDependencyGraph = require("../src/tools/execDependencyGraph");
 main();
 
 function main() {
-  const mode =
-    process.env["TRAVIS_EVENT_TYPE"] === "cron" ||
-    process.argv.includes("--full")
-      ? "FULL"
-      : "BASIC";
+  const mode = process.argv.includes("--full") ? "FULL" : "BASIC";
   execDependencyGraph(makeTasks(mode)).then(({success}) => {
     process.exitCode = success ? 0 : 1;
   });