v2 parser should require newlines between expressions

[moorereason]

Description

TOML expressions should be separated by one or more newlines.

To Reproduce

The following test should not pass but does:

diff --git a/unmarshaler_test.go b/unmarshaler_test.go
index 7d1bd07..fc30367 100644
--- a/unmarshaler_test.go
+++ b/unmarshaler_test.go
@@ -231,6 +231,20 @@ func TestUnmarshal(t *testing.T) {
                                }
                        },
                },
+               {
+                       desc:  "no newline",
+                       input: `a = 1z = 2`,
+                       gen: func() test {
+                               m := map[string]interface{}{}
+                               return test{
+                                       target: &m,
+                                       expected: &map[string]interface{}{
+                                               `a`: int64(1),
+                                               `z`: int64(2),
+                                       },
+                               }
+                       },
+               },
                {
                        desc: "multiline basic string",
                        input: `A = """\

Versions

• go-toml: a533331
• go1.16.3 linux/amd64

Related to #413.

[pelletier]

Thank you for catching this!