various: fix miscellanous typos

Signed-off-by: Patrick Linnane <patrick@linnane.io>

Contributing.md

@@ -41,7 +41,7 @@ will permit you to do:
 $ bundle install
 ```
 
-to get the development dependencies. If you aleady have `hoe` installed, you
+to get the development dependencies. If you already have `hoe` installed, you
 can accomplish the same thing with:
 
 ```sh

lib/diff/lcs.rb

@@ -256,7 +256,7 @@ def sdiff(seq1, seq2, callbacks = nil, &block) # :yields: diff changes
   #
   # The methods for <tt>callbacks#match</tt>, <tt>callbacks#discard_a</tt>, and
   # <tt>callbacks#discard_b</tt> are invoked with an event comprising the
-  # action ("=", "+", or "-", respectively), the indicies +i+ and +j+, and the
+  # action ("=", "+", or "-", respectively), the indices +i+ and +j+, and the
   # elements <tt>A[i]</tt> and <tt>B[j]</tt>. Return values are discarded by
   # #traverse_sequences.
   #
@@ -465,7 +465,7 @@ def traverse_sequences(seq1, seq2, callbacks = Diff::LCS::SequenceCallbacks) # :
   # The methods for <tt>callbacks#match</tt>, <tt>callbacks#discard_a</tt>,
   # <tt>callbacks#discard_b</tt>, and <tt>callbacks#change</tt> are invoked
   # with an event comprising the action ("=", "+", "-", or "!", respectively),
-  # the indicies +i+ and +j+, and the elements <tt>A[i]</tt> and <tt>B[j]</tt>.
+  # the indices +i+ and +j+, and the elements <tt>A[i]</tt> and <tt>B[j]</tt>.
   # Return values are discarded by #traverse_balanced.
   #
   # === Context