Fixes difference_type being mispelled as diference_type.

This fixes the type alias `difference_type` which was mispelled as
`diference_type` in `map`, `set`, `table`, and their transients.

Author: nicola-gigante

immer/map.hpp

@@ -158,7 +158,7 @@ class map
     using mapped_type     = T;
     using value_type      = std::pair<K, T>;
     using size_type       = detail::hamts::size_t;
-    using diference_type  = std::ptrdiff_t;
+    using difference_type  = std::ptrdiff_t;
     using hasher          = Hash;
     using key_equal       = Equal;
     using reference       = const value_type&;

immer/map_transient.hpp

@@ -51,7 +51,7 @@ class map_transient : MemoryPolicy::transience_t::owner
     using mapped_type     = T;
     using value_type      = std::pair<K, T>;
     using size_type       = detail::hamts::size_t;
-    using diference_type  = std::ptrdiff_t;
+    using difference_type  = std::ptrdiff_t;
     using hasher          = Hash;
     using key_equal       = Equal;
     using reference       = const value_type&;

immer/set.hpp

@@ -73,7 +73,7 @@ class set
 public:
     using value_type      = T;
     using size_type       = detail::hamts::size_t;
-    using diference_type  = std::ptrdiff_t;
+    using difference_type  = std::ptrdiff_t;
     using hasher          = Hash;
     using key_equal       = Equal;
     using reference       = const T&;

immer/set_transient.hpp

@@ -40,7 +40,7 @@ class set_transient : MemoryPolicy::transience_t::owner
 
     using value_type      = T;
     using size_type       = detail::hamts::size_t;
-    using diference_type  = std::ptrdiff_t;
+    using difference_type  = std::ptrdiff_t;
     using hasher          = Hash;
     using key_equal       = Equal;
     using reference       = const T&;

immer/table.hpp

@@ -193,7 +193,7 @@ class table
     using mapped_type     = T;
     using value_type      = T;
     using size_type       = detail::hamts::size_t;
-    using diference_type  = std::ptrdiff_t;
+    using difference_type  = std::ptrdiff_t;
     using hasher          = Hash;
     using key_equal       = Equal;
     using reference       = const value_type&;

immer/table_transient.hpp

@@ -42,7 +42,7 @@ class table_transient : MemoryPolicy::transience_t::owner
     using mapped_type     = T;
     using value_type      = T;
     using size_type       = detail::hamts::size_t;
-    using diference_type  = std::ptrdiff_t;
+    using difference_type  = std::ptrdiff_t;
     using hasher          = Hash;
     using key_equal       = Equal;
     using reference       = const value_type&;