Excavator: Upgrades Baseline to the latest version (#59)

###### _excavator_ is a bot for automating changes across repositories.

Changes produced by the roomba/latest-baseline-oss check.

{runtimeCheckDesc}
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.baseline/checkstyle/checkstyle-suppressions.xml

@@ -1,8 +1,7 @@
 <?xml version="1.0"?>
-
 <!DOCTYPE suppressions PUBLIC
-    "-//Puppy Crawl//DTD Suppressions 1.1//EN"
-    "http://www.puppycrawl.com/dtds/suppressions_1_1.dtd">
+    "-//Checkstyle//DTD SuppressionFilter Configuration 1.2//EN"
+    "https://checkstyle.org/dtds/suppressions_1_2.dtd">
 
 <!-- IMPORTANT ECLIPSE NOTE: If you change this file, you must restart Eclipse
  for your changes to take effect in its Checkstyle integration. -->

.baseline/checkstyle/checkstyle.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <!DOCTYPE module PUBLIC
-        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
-        "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+        "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+        "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <!--
     Palantir Baseline Checkstyle configuration.

build.gradle

@@ -25,7 +25,7 @@ buildscript {
         classpath 'com.gradle.publish:plugin-publish-plugin:0.10.0'
         classpath 'com.jfrog.bintray.gradle:gradle-bintray-plugin:1.8.4'
         classpath 'com.netflix.nebula:nebula-publishing-plugin:9.5.0'
-        classpath 'com.palantir.baseline:gradle-baseline-java:0.51.0'
+        classpath 'com.palantir.baseline:gradle-baseline-java:0.51.1'
         classpath 'gradle.plugin.com.palantir.gradle.gitversion:gradle-git-version:0.7.3'
         classpath 'gradle.plugin.org.inferred:gradle-processors:2.1.0'
     }