blocks: add double single quote block recognition (#78)

Nix multi line strings use double single quotes. Adding this to the list
of quotes that indicate blocks.

Signed-off-by: Paul Meyer <katexochen0@gmail.com>

Author: katexochen

goldens/block.in

@@ -137,3 +137,19 @@ some_build_rule(
     src = "one-more-source",
 )
 // keep-sorted-test end
+
+// Nix multi line string
+// keep-sorted-test start block=yes newline_separated=yes
+foo = throw ''
+  Some text here.
+
+  Text has empty lines.
+'';
+
+bar = ''
+  While foo throws, this is just a string
+
+
+    Again, with some spaces here and there.
+'';
+// keep-sorted-test end

goldens/block.out

@@ -137,3 +137,19 @@ some_build_rule(
     src = "another-source",
 )
 // keep-sorted-test end
+
+// Nix multi line string
+// keep-sorted-test start block=yes newline_separated=yes
+bar = ''
+  While foo throws, this is just a string
+
+
+    Again, with some spaces here and there.
+'';
+
+foo = throw ''
+  Some text here.
+
+  Text has empty lines.
+'';
+// keep-sorted-test end

keepsorted/line_group.go

@@ -216,7 +216,7 @@ var (
 	}
 	quotes = []string{
 		`"""`, `'''`, "```",
-		`"`, `'`, "`",
+		`"`, `''`, `'`, "`",
 	}
 )