Adds SQLCipher subspec major version cap which will prevent `pod update` from updating beyond the current major version until explicitly changed in pod subspec.

FMDB.podspec

@@ -40,7 +40,7 @@ Pod::Spec.new do |s|
 
   # use SQLCipher and enable -DSQLITE_HAS_CODEC flag
   s.subspec 'SQLCipher' do |ss|
-    ss.dependency 'SQLCipher'
+    ss.dependency 'SQLCipher', '~> 4.0'
     ss.source_files = 'src/fmdb/FM*.{h,m}'
     ss.exclude_files = 'src/fmdb.m'
     ss.xcconfig = { 'OTHER_CFLAGS' => '$(inherited) -DSQLITE_HAS_CODEC -DHAVE_USLEEP=1', 'HEADER_SEARCH_PATHS' => 'SQLCipher' }