more specific search.

This fixes a bug if the checkout path already has "firebase" in it.
In such cases, the headers won't be copied to firebase.framework.
Making the search more specific fixes it.

Author: vimanyu

app/CMakeLists.txt

@@ -527,11 +527,11 @@ if (IOS)
   # Copy header from source dir "src/include/firebase/*" to destination dir "Headers/*"
   list(APPEND framework_HDRS ${internal_HDRS})
   foreach(hfile ${framework_HDRS})
-    string(FIND ${hfile} "firebase/" pos_firebase)
+    string(FIND ${hfile} "src/include/firebase/" pos_firebase)
     string(COMPARE NOTEQUAL ${pos_firebase} -1 find)
     if(${find})
       string(FIND ${hfile} "/" pos_e REVERSE)
-      math(EXPR pos_s "${pos_firebase} + 8")
+      math(EXPR pos_s "${pos_firebase} + 20")
       math(EXPR len "${pos_e} - ${pos_s}")
       string(SUBSTRING ${hfile} ${pos_s} ${len} dir)
       # file(COPY ${hfile} DESTINATION Headers/${dir})