renamed image files for compat

ch01.asciidoc

@@ -123,19 +123,19 @@ This most basic form of key generation, generates what are known as _Type-0_ or
 
 [[Type0_chain]]
 .Type-0 or Non-Deterministic Keys are randomly generated as needed
-image::images/Type-0 chain.png["Key generation"]
+image::images/type0_chain.png["Key generation"]
 
 ===== Type-1 deterministic (non-random) key chains
 
 [[Type1_chain]]
 .Type-1 Deterministic Keys are generated from a phrase and index number
-image::images/Type-1 chain.png["Key generation"]
+image::images/type1_chain.png["Key generation"]
 
 ===== Type-2 chained deterministic keys
 
 [[Type2_chain]]
 .Type-2 Chained Deterministic Keys are generated from a binary seed and index number
-image::images/Type-1 chain.png["Key generation"]
+image::images/type2_chain.png["Key generation"]
 
 ===== Type-2 hierarchical deterministic keys