Tune JVM options to avoid out of memory issues.

While running the tests locally I hit on OOM exceptions. This commit
fixes the problem by enabling forking and removing unnecessary JVM
options from the `.jvmopts` file. All tests pass now when I run `sbt
tests/test` locally.

Author: olafurpg

.jvmopts

@@ -1,7 +1,6 @@
 -Dfile.encoding=UTF8
 -Xms1G
 -Xmx3G
--XX:MaxMetaspaceSize=512M
 -XX:ReservedCodeCacheSize=250M
 -XX:+TieredCompilation
 -XX:-UseGCOverheadLimit

build.sbt

@@ -217,10 +217,6 @@ lazy val tests = project
     ),
     scalacOptions ++= scalacJvmOptions.value,
     javaOptions += "-Dfile.encoding=UTF8",
-    // Fork in CI to avoid memory limitation issues. Disable forking locally
-    // because ScalaTest error reporting fails with cryptic serialization errors
-    // when forking is enabled.
-    fork := isCI,
     buildInfoPackage := "org.scalafmt.tests",
     buildInfoKeys := Seq[BuildInfoKey](
       "resourceDirectory" -> resourceDirectory.in(Test).value