Ensure Spotless works on Microsoft Windows

This commit is an attempt to ensure that Spotless in the JUnit 5 build
works properly when run on Microsoft Windows. Specifically, line endings
for text files checked out via Git are now forced to LF instead of
allowing automatic conversion to CFLF on Windows. In addition, Spotless
has been configured to use 'UNIX' line endings (i.e., LF).

Issue: #398

.gitattributes

@@ -0,0 +1 @@
+* text eol=lf

build.gradle

@@ -96,6 +96,7 @@ allprojects {
 			eclipseFormatFile rootProject.file('src/eclipse/junit-eclipse-formatter-settings.xml')
 
 			trimTrailingWhitespace()
+			lineEndings 'UNIX'
 			endWithNewline()
 
 			custom 'Lambda fix', { it.replace('} )', '})').replace('} ,', '},') }
@@ -395,11 +396,13 @@ configure(rootProject) {
 			target '**/*.gradle', '**/*.gitignore'
 			indentWithTabs()
 			trimTrailingWhitespace()
+			lineEndings 'UNIX'
 			endWithNewline()
 		}
 		format 'documentation', {
 			target '**/*.adoc', '**/*.md'
 			trimTrailingWhitespace()
+			lineEndings 'UNIX'
 			endWithNewline()
 		}
 	}