chore: update build & README to latest Crystal release

Author: vladfaust

.travis.yml

@@ -1,25 +1,19 @@
-dist: xenial
-language: generic
-sudo: required
+language: crystal
 services:
-  - docker
   - postgresql
-env:
-  - POSTGRESQL_URL=postgres://postgres@localhost:5432/test
-before_install:
-  - docker pull crystallang/crystal:nightly
-before_script:
-  - psql -c 'create database test;' -U postgres
-  - psql $POSTGRESQL_URL < db_spec/pg/migration.sql
 script:
-  - docker run -v ${PWD}:/x -w /x crystallang/crystal:nightly bash -c "/usr/bin/shards install"
-  - docker run -v ${PWD}:/x -w /x crystallang/crystal:nightly bash -c "/usr/bin/crystal spec"
-  - docker run -v ${PWD}:/x -w /x --net=host -e POSTGRESQL_URL=$POSTGRESQL_URL crystallang/crystal:nightly bash -c "/usr/bin/crystal spec db_spec/"
-  - docker run -v ${PWD}:/x -w /x crystallang/crystal:nightly bash -c "/usr/bin/crystal docs"
+  - crystal spec
+  - env POSTGRESQL_URL=$POSTGRESQL_URL crystal spec db_spec
+  - crystal docs
 deploy:
   provider: pages
   skip_cleanup: true
   github_token: $GITHUB_TOKEN
   on:
     branch: master
   local_dir: docs
+before_script:
+  - psql -c 'create database test;' -U postgres
+  - psql $POSTGRESQL_URL < spec/migration.sql
+env:
+  - POSTGRESQL_URL=postgres://postgres@localhost:5432/test

README.md

@@ -1,5 +1,3 @@
-> ⚠️ Master branch requires Crystal master to compile. See [installation instructions for Crystal](https://crystal-lang.org/docs/installation/from_source_repository.html).
-
 # Atom::Model
 
 [![Built with Crystal](https://img.shields.io/badge/built%20with-crystal-000000.svg?style=flat-square)](https://crystal-lang.org/)

shard.yml

@@ -4,7 +4,7 @@ version: 0.5.0
 authors:
   - Vlad Faust <mail@vladfaust.com>
 
-crystal: master
+crystal: 0.27.0
 
 dependencies:
   time_format: