Mention Byte Buddy as cglib alternative in the documentation

[Vampire]

This change is 

[codecov]

Codecov Report

Merging #1020 into master will increase coverage by 0.13%.
The diff coverage is 95.65%.

@@             Coverage Diff              @@
##             master    #1020      +/-   ##
============================================
+ Coverage        74%   74.14%   +0.13%     
- Complexity     3449     3471      +22     
============================================
  Files           385      385              
  Lines         10660    10677      +17     
  Branches       1301     1307       +6     
============================================
+ Hits           7889     7916      +27     
+ Misses         2309     2300       -9     
+ Partials        462      461       -1

Impacted Files	Coverage Δ	Complexity Δ
...core/src/main/java/spock/util/environment/Jvm.java	91.17% <100%> (+16.17%)	38 <21> (+13)	⬆️
...ockframework/mock/constraint/TargetConstraint.java	93.33% <85.71%> (-6.67%)	8 <1> (+4)
...ckframework/mock/runtime/ByteBuddyMockFactory.java	82.69% <0%> (ø)	9% <0%> (ø)	⬇️
...ockframework/mock/runtime/JavaMockInterceptor.java	92.3% <0%> (ø)	16% <0%> (ø)	⬇️
...e/extension/builtin/PendingFeatureIfExtension.java	76.47% <0%> (ø)	6% <0%> (ø)	⬇️
...va/org/spockframework/mock/runtime/MockObject.java	82.85% <0%> (-8.58%)	22% <0%> (-1%)
.../spockframework/util/StringMessagePrintStream.java	83.07% <0%> (ø)	23% <0%> (ø)	⬇️
...rc/main/groovy/spock/util/matcher/IsCloseTo.groovy	87.5% <0%> (ø)	6% <0%> (ø)	⬇️
.../spockframework/gentyref/GenericTypeReflector.java	35.23% <0%> (ø)	28% <0%> (ø)	⬇️
.../spockframework/builder/CollectionSlotFactory.java	88.88% <0%> (ø)	6% <0%> (ø)	⬇️
... and 16 more

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[leonard84]

Actually byte-buddy is the main and cglib the backup, if both are on the classpath, byte-buddy is used.

[Vampire]

Actually byte-buddy is the main and cglib the backup, if both are on the classpath, byte-buddy is used.

I swapped the two in the sentence if that was what you meant.
If not, please be more specific.