Make sure SIP numbers are used exactly once, and proposals use exactly one number.

Author: julienrf

_sips/sips/2016-09-09-inline-meta.md

@@ -1,6 +1,6 @@
 ---
 layout: sip
-title: SIP-28 and SIP-29 - Inline meta
+title: SIP-28 - Inline meta
 vote-status: dormant
 vote-text: This proposal needs an owner.
 permalink: /sips/:title.html

_sips/sips/2017-07-12-right-associative-by-name-operators.md

@@ -1,6 +1,6 @@
 ---
 layout: sip
-title: SIP-34 - Right-Associative By-Name Operators
+title: SIP-39 - Right-Associative By-Name Operators
 vote-status: complete
 vote-text: This SIP has been implemented in Scala 2.13.0 and Scala 3.0.0
 permalink: /sips/:title.html

_sips/sips/2017-11-20-byname-implicits.md

@@ -1,6 +1,6 @@
 ---
 layout: sip
-title: SIP-36 - Byname implicit arguments
+title: SIP-31 - Byname implicit arguments
 vote-status: complete
 vote-text: This SIP has been implemented in Scala 2.13.0 and Scala 3.0.0
 permalink: /sips/:title.html