Add test for trailing blank lines

Check for blank lines at end of file.

Author: stomar

lib/linter.rb

@@ -64,6 +64,7 @@ def check
       errors[doc] << "missing or invalid lang variable"  if doc.lang_invalid?
       errors[doc] << "lang variable not matching file location"  if doc.lang_not_matching_filename?
       errors[doc] << "no newline at end of file"  if doc.no_newline_at_eof?
+      errors[doc] << "blank line(s) at end of file"  if doc.blank_line_at_eof?
       errors[doc] << "wrong line breaks (CR/LF)"  if doc.crlf_line_breaks?
 
       unless WHITESPACE_EXCLUSIONS.include?(doc.filename)

lib/linter/document.rb

@@ -91,6 +91,10 @@ def no_newline_at_eof?
       !content.end_with?("\n")
     end
 
+    def blank_line_at_eof?
+      content.end_with?("\n\n")
+    end
+
     def trailing_whitespace?
       content.match?(/ $/)
     end

test/md_errors/en/11_blank_line_at_eof.md

@@ -0,0 +1,8 @@
+---
+layout: page
+title: "Page"
+lang: en
+---
+
+Content
+

test/md_errors/en/12_blank_lines_at_eof.md

@@ -0,0 +1,10 @@
+---
+layout: page
+title: "Page"
+lang: en
+---
+
+Content
+
+
+

test/output_errors.txt

@@ -20,6 +20,10 @@ en/09_lang_variable_wrong.md
 en/10_multiple_errors.md
   missing or invalid lang variable
   trailing whitespace
+en/11_blank_line_at_eof.md
+  blank line(s) at end of file
+en/12_blank_lines_at_eof.md
+  blank line(s) at end of file
 en/_posts/2000-01-01-old-lang-variable-nil.md
   missing or invalid lang variable
 en/_posts/2000-01-02-old-translator-variable-wrong-type.md