Test that digits in local-time must always have a width of 2

Ref: BurntSushi/toml#320

tests/invalid/datetime/impossible-date.toml

@@ -1 +1,2 @@
+# No months with 50 days.
 d = 2006-01-50T00:00:00Z

tests/invalid/datetime/no-leads-with-milli.toml

@@ -1 +1,2 @@
+# Day "5" instead of "05"; the leading zero is required.
 with-milli = 1987-07-5T17:45:00.12Z

tests/invalid/datetime/no-leads.toml

@@ -1 +1,2 @@
+# Month "7" instead of "07"; the leading zero is required.
 no-leads = 1987-7-05T17:45:00Z

tests/invalid/datetime/no-secs.toml

@@ -1 +1,2 @@
+# No seconds in time.
 no-secs = 1987-07-05T17:45Z

tests/invalid/datetime/no-t.toml

@@ -1 +1,2 @@
+# No "t" or "T" between the date and time.
 no-t = 1987-07-0517:45:00Z

tests/invalid/datetime/time-no-leads-2.toml

@@ -0,0 +1,2 @@
+# Leading 0 is always required.
+d = 01:32:0

tests/invalid/datetime/time-no-leads.toml

@@ -0,0 +1,2 @@
+# Leading 0 is always required.
+d = 1:32:00

tests/invalid/datetime/trailing-t.toml

@@ -1 +1,2 @@
+# Date cannot end with trailing T
 d = 2006-01-30T