Improved sanitizing of configuration names which have a number prefix.

CHANGELOG.md

@@ -61,6 +61,9 @@ To install or update CocoaPods see this [guide](http://docs.cocoapods.org/guides
   [Eloy Durán](https://github.com/alloy)
   [#2723](https://github.com/CocoaPods/CocoaPods/issues/2723)
 
+* Improved sanitizing of configuration names which have a number prefix.
+  [Steffen Matthischke](https://github.com/HeEAaD)
+  [#2700](https://github.com/CocoaPods/CocoaPods/pull/2700)
 
 ## 0.34.4
 

lib/cocoapods/project.rb

@@ -209,7 +209,7 @@ module Pod
     #
     def add_build_configuration(name, type)
       build_configuration = super
-      values = ["#{name.gsub(/[^a-zA-Z0-9_]/, '_').gsub(/(^[0-9])/, '_\1').upcase}=1"]
+      values = ["#{name.gsub(/[^a-zA-Z0-9_]/, '_').sub(/(^[0-9])/, '_\1').upcase}=1"]
       settings = build_configuration.build_settings
       definitions = Array(settings['GCC_PREPROCESSOR_DEFINITIONS'])
       values.each do |value|